# Honda EU2000i Loses RPM & Voltage output Only After 3 minutes Under Full Load



## Micro-Air

Hi everyone. I'm a new member here. I've been battling this problem for a customer for quite some time, and before I tear this engine apart, I wanted to get some input from any experts out there. Here is what's going on. I hope you are all up for this challenge! :tango_face_smile_bi

Without getting into the details of our business, we have a lot of experience with the Honda EU2000i generator. We literally have hundreds of customers who can operate this generator at the top of its 2000VA maximum output for hours on end, providing it doesn't run out of gas. 2000VA is of course 16.7A @120VAC. I've done a lot of research into the Honda, and using an aftermarket RPM meter, I know that the ECO mode idle is 3000RPM, the ECO mode off idle is 4300 RPM (which provides about 1600VA), and the full load RPM for 2000VA is 5000RPM. Under full load, every Honda EU2000i we've ever tested can provide about 115-120V at upwards to 16A without any problem, and do it continuously without skipping a beat. Typically, the voltage output is about 125VAC when unloaded.

Enter the problem generator owned by one of our customers. His name is Ron. Ron's generator will start off providing the full load amperage up to the 16.7A limit (say 16A for sake of testing), and its motor will reach and stabilize at the 5000RPM like all of the other Honda generators under the same test condition. Then, after about 3 to 4 minutes of operation, Ron's generator will start dropping in RPM. I know the throttle and its associated motor servo very well since we replaced Ron's carburetor with a brand new one a few weeks ago when this all started. The THROTTLE IS WIDE OPEN AND UP AGAINST ITS STOP for the entire time this RPM reductions starts and continues to take place. So, we know its not a control system issue. Ron's generator will then slowly drop in RPM, going as low as about 4400 RPM, and if the load is kept on, the output voltage of course will also start dropping. At no time is the load brought above the 2000VA limit (16.7A), so the generator never declares an overload (lights its LED). The voltage will eventually drop to about 98V if I keep the load up at about 15A. I don't have a precise load bank device, so my ability to adjust the load precisely as the voltage drops gets difficult since the load devices I'm using draw less current as the voltage drops.

Anyway, NO OTHER HONDA EU2000i THAT WE'VE EVER TESTED DOES THIS under the same test conditions. They all can hold their 5000 RPM rock solid, keep their output voltage in the 115-120V range, and keep their output current at or above 16A (to just below the 16.7A max limit).

So, over the past several weekends of working on this, I've eliminated the obvious causes of fuel, air, and spark. As mentioned above, the carburetor is brand new, the spark plug is new, the stator and rotor, and the various auxiliary windings were all tested per the service manual (voltage outputs at RPM and resistances). The fuel filter was changed, and the problem still occurs even when the air filter is removed (thus eliminating that). The valve clearances have already been checked and the exhaust valve was slightly adjusted (increased); it made absolutely no difference. 

The only thing left is engine compression. I purchased a compression tester and did some side-by-side testing with Ron's Honda. I found that when it was hot, it had compressor down in the 35PSI range (40 when cold). A "good" Honda EU2000i that I tested alongside of it was in the 45PSI range when hot, and 50PSI when cold. The service manual of course states that the compression should be 71PSI when cold, but I have yet to measure a Honda with that much compression. Bottom line though, the "good" Honda with 50PSI when cold passed the above sustained load test without any issues.

So, at this point, I'm faced with going after the obvious causes of compression loss when hot: 1) Piston rings, and 2) valves. 

Based upon the above, and the experience of those in this forum, what is the most likely cause here and does such a problem even ever happen with these seemingly bullet-proof Honda Engines? Since the design of the Honda EU2000i engine makes it difficult to inspect the valves since the head and cylinder body are a single piece (no removable head), I'll have to take out the piston to inspect the valves and the top of the cylinder head. I'm not a guru on re-lapping valves and removing and installing pistons with rings, but I can bring my engineering abilities to bear, learn what it takes, gather the right specialty tools, and do it. But before I do, I wanted to get some opinions and recommendations. Perhaps I'm overlooking some other cause that I should check first?

Any input would be appreciated. Thank you very much in advance for any advice.


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## thehandyman1957

Ok, so I have couple of questions. When it is running and losing rpm's during heavy load, do you notice any excess blow by from the crank case into the carb? I.E. loss of compression from a bad ring type thing. Second, do you notice any sort of miss or harsh running conditions during this issue? I.E. some sort of valve leakage?

Beyond those two items, you say you have eliminated the lack of fuel issue. What steps did you take to eliminate the possibility?

Have you been able to find the limit ampage the generator can handle before running into this issue. I.E. will it run fine under say a 10 amp load?

My thought here is that it could be an issue with the lower compression but if that is the case I would think you would be getting some extra blow by from the crank case. 

Perhaps a leak down test might help you determine what you need to know.


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## Micro-Air

thehandyman1957 said:


> Ok, so I have couple of questions. When it is running and losing rpm's during heavy load, do you notice any excess blow by from the crank case into the carb? I.E. loss of compression from a bad ring type thing. Second, do you notice any sort of miss or harsh running conditions during this issue? I.E. some sort of valve leakage?
> 
> Beyond those two items, you say you have eliminated the lack of fuel issue. What steps did you take to eliminate the possibility?
> 
> Have you been able to find the limit amperage the generator can handle before running into this issue. I.E. will it run fine under say a 10 amp load?
> 
> My thought here is that it could be an issue with the lower compression but if that is the case I would think you would be getting some extra blow by from the crank case.
> 
> Perhaps a leak down test might help you determine what you need to know.


Thank you very much, Handyman1957. My boss is a motorcycle engine builder/racer from decades gone by, and he has been stating the same things about the (unlikely) possibility of the valve and/or piston leakage. If I do not notice any blow-by/blow-back through the intake, then the intake valve can't be leaking. Also, if I don't notice anything abnormal coming out of the crankcase breathers, then I assume the rings aren't likely bad either. The exhaust valve might be the only one that would be hard to tell, but lots of soot, a clogged spark arrestor, and muffler carbon, and maybe some backfiring might be evident in that case. Honestly, I would have to say that I have NONE of the above symptoms. So, perhaps I am barking up the wrong tree as the boss is suggesting. I appreciate your making me think through this again.

What I do notice at the 3 minute point when the RPM begins to drop is a subtle change in the tone of the engine. Obviously, that is partly because of the RPM beginning to drop. I wouldn't say the engine is running "rough" at this point, but it certainly is no longer "smooth" and steady. The drop in RPM is gradual and slow, and it takes another 2 to 3 minutes to bottom out in the low 4000s, where it fluctuates slowly. 

Like you, the boss also suggested a leakdown test instead of a compression test. I opted for the latter tester because it was cheaper to obtain. That may have been a mistake as well. Before tearing into anything I should probably consider doing this test somehow. I think I can rig something up with my refrigeration equipment. I'll go to 90PSI like the guy in the YouTube video did.

The generator can maintain about 14A of load without experiencing this drop in RPM after a few minutes of operation.

Lastly, the way I eliminated the fuel starvation cause was simply by the replacement of the carburetor and the fuel filter. I realize that there is a fuel pump, and high load means high fuel consumption, so the bowl could be falling behind. That might result in a leaner mixture, which does cause any engine to run hotter. I'm not sure what to do about this though. How can I inspect and/or service this fuel pump, or at least verify that the fuel flow is adequate for the high load condition?

Lastly, one symptom I forgot to mention, the RPM will go back to 5000RPM if I remove the high load, let the RPM drop back to say 3000 (ECO mode ON lowest speed) for a few minutes, then reapply the full load. I figured (and perhaps made the bad assumption) that the engine was cooling off during this time, thus allowing it to perform again when returning to high load for the couple minutes it seems to be able to handle. Maybe the fuel level in the bowl is recovering during this time instead and that is the cause? 

Any input would be appreciated on how I could do a better job of verifying the maximum fuel flow. Thanks again.


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## thehandyman1957

Ahh, I believe you have answered your own problem right there. It now makes sense to me. It's very much likely your fuel pump is not able to keep up with the demand. The fact that you can relieve the load and after a few minutes be able to run it again at full load is the key indicator that your carb is leaning out. It sounds to me like the pump is just at the edge of failure and you are seeing this in the form of lack of full fuel pressure at full load. I sure there is a tool to see the pressure but the silly thing is, it's only $26 for a OEM fuel pump on ebay.

Genuine Honda 16700-ZT3-013 Fuel Pump Fits GXH50 GXH50U EU1000i EU2000i OEM | eBay

I would definitely replace the pump before I dig into the motor.

Of course a leak test wouldn't hurt if you could do it, but if you have to spend money to make that happen I would wait till the new pump is in and then tackle that job if the problem still exists.

Good luck.


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## exmar

Know nothing about Honda's, but agree with Handyman. Thinking about it, it runs under full load for three minutes, then acts up. Gotta be ignition or fuel. Compression testing, leak down, etc. look at physical metal components and head gasket. Find it hard to believe that Metal can stand the load for three minutes, then "sort of" break down, then recover, etc. ? $26 vs a teardown, I'd take that bet any day. Again, know nothing about Honda's, but if I replace a fuel pump on anything, I also replace the fuel lines and clean or at least verify the fuel tank outlet is clear. Partially obstructed fuel ine can act like a bad fuel pump.


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## Micro-Air

Thank you Handyman and Exmar. I ordered an aftermarket fuel pump since I could get it in one day, and that turned out to be a mistake. It didn't fit properly. I tried it anyway, and it made no difference. I tested the existing pump, and checked all the fuel lines since I had the generator's skins completely removed today for better access to everything. I found no issues and the old pump appears to be working fine. I'll replace it anyway though.

Beyond the above, I ran a whole bunch of tests today over the course of many hours. Given what I observed, I'm once again having a tough time attributing fuel starvation to the RPM symptoms. One would think that if the fuel bowl were falling behind at high load, it would eventually empty and I would then notice more dramatic changes in RPM (drop-outs and surges). That never happens. The RPM drops 10 revs at a time (per the digital meter), slowly and gradually, starting from 5000, and the motor seems to be running smoothly throughout. With the skins off today and the motor fully exposed, I was able to watch and listen to the motor more closely during this RPM loss. It really doesn't seem to be running any rougher. During the first couple minutes, the RPM can attain 5000, and the throttle isn't quite wide open and I can see the servo motor regulating it. Then, slowly the throttle has to be opened more and more, eventually ending up pinned against the stop. It is at that point that the control system has obviously run out of dynamic range, and then the RPM starts it slow and steady drop. After about 5 more minutes, the RPM seems to settle at around 4400RPM, and with the load at about 14.3A. For comparison, last week I tested about 6 or 7 Honda EU2000i generators at an RV rally and was able to verify that they all held 5000 RPM and 16A+ indefinitely (5-10 minutes in the tests I ran). I therefore know these Honda's can do this. Why this one in particular can't is still a mystery.

I'll order the OEM fuel pump, but I don't expect it to resolve the issue. The gas tank was already cleaned and the fuel filter already replaced (as part of this debug process which started weeks ago). I'm now planning on purchasing another generator for our customer to perhaps be able to swap and keep this one for further analysis to the root cause.


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## thehandyman1957

Well, my thought process on the fuel pump is this. As the motor is requiring more fuel the pump is pumping but slowing down on delivery but not stopping. Therefore, as the bowl gets lower the motor starts slowing down thus requiring more fuel till it can't get anymore from the throttle. 

Perhaps this is fuzzy logic but it's the only thing that makes sense. If this were a metal fatigue issue, I.E. rings or valves then how would it be able to recover without completely cooling the engine back down first. If the engine runs perfect even when slowing down then it leads me to believe that it must be a fuel issue. I've never heard of a valve or rings being able to recover in such a small period of time. Especially without showing some sort of running issue like excessive blow by from the crank case or popping or spitting as was the case for me when I had a leaky exhaust valve or simply never having enough power.

I will be looking forward to what happens when you do replace the fuel pump.

One more dumb question, when running into this issue have you tested to see if there is a vacuum in the fuel tank? I.E. the pressure release mechanism is plugged and causing a vacuum in the tank thus making it harder for the pump to pull fuel?

Next time you try a test, pull the fuel cap off when it starts to rpm down and see if there is a vacuum.


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## exmar

Plugged gas cap? Life couldn't be that cruel!!!


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## Micro-Air

Thanks again, guys. Not only did I remove the gas cap during the "problem" yesterday as a test, I took it all apart to clean it. I was partly curious how it worked anyway, and noticed that it really doesn't pass that much air when in the "ON" position. In any event, the cap was not the cause.

Although I am still tore, I do like the rationale of your fuel starvation theory, Handyman. I ordered the OEM fuel pump last night, but now I have to wait for it to ship cross-country. I wish there was a way to test the fuel flow as the cause without having to wait. 

The fuel line routing of the Honda EU2000i does end up requiring the pump, but there may be a workaround for testing purposes. The bottom of the fuel tank is slightly below, but almost level with the fuel bowl of the carburetor about 8-10" away. The fuel filter is integral with the fuel tank exit fitting. The fuel line then goes down, makes a 180 deg turn and connects to a small petcock at the back of the on/off ignition switch. This rotary switch turns off/on the ignition and turns off/on the fuel at the same time. The fuel line then exits the petcock and goes straight up and into the input side of the fuel pump after a 45-deg turn. The inlet of the fuel pump is slightly below the level of the tank exit, so gravity should at least bring fuel to that point. The outlet of the fuel pump then goes pretty much straight across the side of the generator/engine (horizontally with maybe a few degrees of incline) into the carburetor about 6" away, after a few more turns. I had traced the entire thing yesterday when I was inspecting hoses for blockage, and although I saw that the hoses were pristine on the inside, there were opportunities for hoses to kink. If the fuel pump were marginal, then I could certainly see why it might fall behind.

So, as a test I was thinking that I could temporarily mounted or hold the fuel tank well above the height of the carburetor, effectively doing gravity feed straight into the carburetor without the pump (or petcock). I'd could keep the cap loose enough to avoid any issues with back pressure. I can't imagine that the float and valve in the fuel bowl would require any more pressure than this to operate. What do you think?


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## Micro-Air

*No go with new OEM fuel pump and leak test passed!*

UPDATE:

I received the OEM fuel pump today and also received a cheap leakdown tester a couple days ago. I had picked up an almost brand new Honda EU2000i on Monday from a pawn shop. It was pretty much out-of-the-box.

The new Honda passed the load duration test fine, holding 5000 RPM for over 10 minutes without any fluctuation. I ran a leakdown test on it and it wasn't that great. Probably because it isn't broken in yet. 

I then installed the new OEM fuel pump on the problematic Honda and ran the load test again. There was no improvement in the load duration test as I expected. The RPM held at 5000 for about 3 minutes, then started its slow decline. I ran the leak down test afterwards and to my surprise it was 9-12%, which is considered quite low. I could not hear any pressurized air escaping on the old Honda during the leakdown test like I could on the new Honda. The old Honda was as tight as a drum, although it had cooled about 5 minutes by the time I got everything apart to conduct the leakdown test.

So, I'm back to where I was. At this point, given all that I have done, I really feel like I've eliminated fuel, spark, air, and goodness maybe now even compression! What else could it be? 

One other observation that I have with the problematic Honda is the heat of the engine air exhaust and the heat of the main (muffler) exhaust during the load test. The problematic Honda seem to MUCH run hotter than any other Honda I've ever tested. Substantially more. There is good air flow from the fan, and everything is obviously intact, free flowing, and clean as a whistle since I've had this disassembled almost completely several times. I cannot explain what could cause it to run so hot. This may be related to the problem. 

Where do I go from here? Thanks in advance.


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## Micro-Air

TEST:

2 of my last replies to this post have been withheld for moderator review. I'm not sure why. This post is short as a test.

I do have tests results from the OEM fuel pump and leakdown compression test. I will report on those if this post seems to make it through.


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## Micro-Air

Okay. It looks like it's working. I'll try to keep this brief since I think when I write a lot, it triggers the withholding for moderator review.

I received the new OEM fuel pump and a leakdown compression tester this week. I also purchased an almost new Honda EU2000i for the customer. 

New Honda Test Results: Passes load endurance test with flying colors. Maintained over 16A for over 10 minutes. Held RPM solid at 5000. Leakdown compression test was actually quite bad since I don't think its broken in yet! I could actually hear the compressed air escaping out of the exhaust and intake at TDC.

Problematic Honda Further Test Results: New fuel pump made absolutely no difference in the load endurance test results. It still did what it always does maintained the 16A output and 5000RPM for about 3 minutes, then started its slow decline thereafter. A Leakdown compression test results were phenomenal! 9-12%. I could not hear any compressed air escaping out anywhere on this old Honda at TDC! 

One thing I do notice is the problematic Honda really does seem to have very hot exhaust cooling air and very hot muffler exhaust. This may be related to the problem.

So, I really now feel like I have done a thorough job of eliminating fuel, spark, air, and even compression! What else could be the cause of this mysterious loss of power and RPM after 3 minutes of full load operation?


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## thehandyman1957

This is a strange beast to say the least. 

I'm going to throw one more idea out at you. You say it has a very hot exhaust?

Is it possible that the muffler is perhaps somewhat plugged, I.E. the spark arrester? 

A bad exhaust valve would not cause a hot muffler, but lack of proper flow out the muffler would. 

Kinda like having a clogged catalytic converter.

And a over heated motor would lose power as it got hotter and as it cooled regain that power.

Just a thought.


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## Micro-Air

Thanks again for the suggestion. Long ago in the debug process, thinking along the same lines, I did clean and then try running without the spark arrestor. I was going to even try to run without the muffler, but because removing the spark arrestor didn't even make the slightest improvement, I didn't want to bother the neighbors with the extreme noise.

Reading more online, I am now wondering if there is a lubrication problem. I know oil is reaching the cam and the top of the valves since whenever I adjusted their clearances - which I did many times as as experiments - they were always well oiled. I'm not sure what's going on in and around the piston though. I'm delivering the new Honda to the customer tomorrow, and will run a side-by-side test to see what the temperatures actually read out with my laser IR temp gun. I'll be keeping the old Honda for further study. 

Last thought, I watched a YouTube video about a week ago of a person who tore down a Honda and had found cracks in the single-piece, cylinder/head body. I'm wondering if something isn't going on around the intake, resulting in intake air leakage when the engine heats up, driving the mixture more lean, thus heating it up further. It recovers within a minute of running at idle from whatever is going wrong, and it will then run at 5000 RPM again, albeit for a shorter period of time (since it's already hot).


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## thehandyman1957

That actually was my first thought, but I did not know you had checked the muffler. 

That would also explain the heat issue.


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## Osviur

Hi all,

This is a generator with a included inverter unit, this inverter takes power from the engine through the alternator and after rectifying the AC power produced, converts it to AC 60 Hz 120 V up to 2000 VA, using a set of MOSFETS in a bridge configuration.
If there is a lack of cooling in said Mosfets they can start in a thermal run down condition, failing to commutate and taking more current for the same load, increasing the heating in the dissipators.
The change in the sound tone may be for a excessive load for the engine as it were supplying more than 2000 VA, lowering the voltage produced the current lowers too, and the MOSFETS then can supply this lower load.

This is just one cause to produce a fail in the inverter, failing capacitors or MOSFETS may alter the correct operation too.
To determine this possibility of failure you can measure the alternator output current in any of the AC output wires during the critical 3 minutes period at full load, or replace the inverter asm. and try again.

Regards


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## thehandyman1957

The only problem with your idea is that the OP stated this.



> Then, after about 3 to 4 minutes of operation,* Ron's generator will start dropping in RPM*. I know the throttle and its associated motor servo very well since we replaced Ron's carburetor with a brand new one a few weeks ago when this all started. The THROTTLE IS WIDE OPEN AND UP AGAINST ITS STOP for the entire time this RPM reductions starts and continues to take place. So, we know its not a control system issue. Ron's generator will then slowly drop in RPM, going as low as about 4400 RPM, and if the load is kept on, the output voltage of course will also start dropping.


I think it would be safe to assume at this point that it's not an inverter issue as it does try to get more RPM's when the motor starts to drop in power. The only time he see's voltage drop is when the RPM's get to low and it's at full stop on the throttle.


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## Osviur

Yes, 3 or 4 minutes at full load may be the time needed to increase the transistors temperature at a point where they are not more stable…….May be…….

I think that it is like driving, and slowly applying brakes. The engine will not withstand that load and decrease RPMs even maintaining a wide open throttle .

It is important to note that this is a 3 phase generator with 3 non fused lines, connected directly to the inverter. Its output is 2000 VA at 120 volts, the input must be a 10% higher, so the generator output is about 2200 VA trough 3 lines (3 phase generator) : Red, white, blue wires. Assuming that the inverter works directly with the generator line voltage, the line current would be:

2200 VA/ 120 V = 18.3 A for single phase, but this is a 3 phase gen, so the line current will be:
18.3 A / 1.73 (3 Sq root) = 10.5 A per line.

This at full resistive load, during the first 3 minutes, then to compensate the extra heat due to the inverter failure, this current will increase and the engine overloaded will be unable to maintain 5000 RPM at this torque demand and will reduce RPM, this reduce voltage output and this the current up to a point where there is a balanced condition. More or less something like that.


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## thehandyman1957

Ahhh, now it's much clearer. This makes sense. Thank you for the understanding. 

This is the part where I am a bit clueless. The mechanical makes sense to me but I don't have the understanding for the high end electronics. 

I did not realize that the inverter would actually require more power than the generator could actually supply. But after your explanation I can see how this could be the case. 

I think he has pretty much gone over everything else that makes sense. The extra heat at the exhaust could simply be from the generator working so hard to keep up with this extra load.


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## Micro-Air

Good morning, gentlemen. Sorry for the delay in responding. I'm only able to work on this project during my "working" weekends.

I intend to run Osviur's test this weekend. Thank you for the suggestion. I concur that if the load on the 3-phase alternator feeding the inverter goes up, so does the load on the engine. That in turn could cause a slow decrease in RPM if the alternator load is climbing due to a problem with the inverter drawing too much current internally due to a variety of issues (e.g. IGBT 3-phase H-Bridge cross-conduction). I'm going to put a clamp-on ammeter on one or more of the 3-phase alternator output wires feeding the inverter, and simultaneous monitor the other things I have been monitoring (output voltage, current, and RPM), and then reproduce the problem. If the current exiting the 3-phase alternator's stator goes up as the generator heats up, then Osviur's theory that the inverter may be developing an issue at higher temps is likely true. If the output from the alternator's stator stays steady during the "working" 3-minutes and then starts dropping with the RPM, then that would prove it is not the inverter overloading the alternator due to some internal inverter issue. 

Hopefully I'll have results to report by tomorrow. If the test fails to prove that the inverter is the cause, then the darn engine is coming apart next!


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## Osviur

..........And just in case, check for a balanced output voltage from the alternator to discard an internal insulation failure in the coils or between them......

Regards and good luck !


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## Micro-Air

*Alternator test results indicate that it is not the cause*

I rigged up some wire extensions for the 6-position plug that connects the 3-phase alternator and single-phase sub-winding outputs to the inverter. This allowed me to measure current as well as voltage during operation. I then ran the test to see what happens to the 3-phase alternator output during the high output load condition (~16A @120VAC) that causes the RPM to slowly decay from 5000 down to about 4400. My observations were that the voltage and current for each phase of the alternator followed the inverter's output voltage and current, almost exactly proportionally. The inverter's output started at about 120VAC at 16A at 5000RPM (close to full throttle, then soon at full throttle), and ended up at about 108V at 14.5A at 4400RPM (still full throttle). The output voltage from the alternator started at about 190V for all 3 phases at about 8.2A, and as the time elapsed it stayed steady until the RPM began to drop, at which point the alternator output voltage and current started dropping as well. They ended up at about 176V at about 7.3A. I observed no increase in the alternator output currents or odd changes in voltage as the generator heated up during its 3 minutes of "good" operation, before the RPM began is slow decay downward.

I therefore conclude that it is not the inverter that is applying an increased load on the alternator, thus increasing the load on the engine itself, dragging down the engine RPM. Something else is causing the engine to lose power after the 3 minutes expires, even though the throttle is wide open.

I will be disassembling the engine over the next few weeks. I'll be paying close attention to the mechanical governor, piston, rings, valves and general condition of the cylinder casting.


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## Osviur

Ok Micro-Air, very interesting the data collected during your test, so the electrical parts are operating as expected, let's them rest and, as you say, it's the time for the engine. 

Best regards


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## lexy2670

very interesting to hear that....


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## Osviur

It would be interesting too, to know the frequency generated at 5000 RPM, but I could see that your VOM has not that feature. May be in another opportunity.

Regards


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## Micro-Air

Osviur said:


> It would be interesting too, to know the frequency generated at 5000 RPM, but I could see that your VOM has not that feature. May be in another opportunity.


It does, but yellow "Hz" label near the AC volts selection was just dirty

I just wanted everyone to know that I'm getting closer. I was delayed due to work, other projects, and associated disasters. Slowly (yawn) disassembled the Honda EU2000i. I really love the way they designed this thing. Quite the puzzle, but very straightforward. Borrowed a dumb puller tool this morning to get the rotor and stator off. I'm ready to drain the oil and begin exploratory surgery. I can already see that the exhaust valve stem seems very oily, but I don't see any evidence of blow-by on the top side of the valve stem near the rocker arms and cam. I'm still placing my bets on piston rings. We shall see...


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## thehandyman1957

Quite interested in what you find. Keep us updated : )


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## Micro-Air

*Engine Apart*

Okay. It's apart. I'm fully committed now! :tango_face_wink:

Initial impressions are the thing is quite clean. The carbon deposits are nothing out of the ordinary in my opinion. The combustion chamber looks fine as do the valves. The piston rings do have wear though. Their end gap measurement has them at the end of the specification, but well within their "service life" as called out in the service manual. Obviously I'm going to replace them anyway. I really cannot see anything else wrong. What I thought was oil on the exhaust valve shaft may not have mattered since that valve sleeve intentionally has no seal, unlike the intake valve sleeve (which has a plastic seal). A little oil on the exhaust valve shaft after sitting idle for a while is probably normal. The previous compression and leakdown tests were good, but at high temperatures, I have a feeling that cylinder wall expansion could be causing a compression loss past the rings. The second ring in particular has completely worn off its asymmetric "taper". The top compression ring has evidence of wear on its outside edge and discoloration on its underside which may be due to some blow-by, although I don't really know what is "normal". 

The service manual calls out a procedure to wire brush the combustion chamber with the valves in place and closed of course. I'm not sure this will do much of anything except maybe aid in heat dissipation. Same is true for the very top of the piston which does seem to have a fairly thick coat of carbon. I'll probably clean up both in any case, being careful not to scratch the cylinder walls or the sides of the piston.

A bunch of parts have now been ordered including the piston rings, some o-rings, shaft oil seal, and some other miscellaneous items. Hopefully I'll have everything in time for a Labor Day Weekend reassembly project.


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## thehandyman1957

Wow, and I thought my valve job was a lot of work....Oh and on a silly note, I have the exact same flashlight : )


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## Micro-Air

*New Rings Had Zero Effect - Exhaust Valve Next*

*Summary*
Well, it's taken me a couple days to recover from the disappointment. I was having fun with the teardown, painstaking and careful carbon deposit cleanup, and parts replacement - the piston rings, oil seal, an o-ring, and some gaskets. The reassembly went well too, including the application of the Honda Bond 4 gasket maker/seal. I was also proud of my work when only after a few pulls to fill the fuel bowl and maybe 2 or 3 pulls to choke it, the thing started right up on the first ignition-on pull after that. Sadly though, the full load test results couldn't have been more identical. It ran for 3 minutes again at 5000 RPM, 90% throttle, then after the throttle slowly climbed to hit the wide-open stop, the RPM slowly began its gradual decline down to the 4400 range. Most disappointing.

*Where to next?*
After much contemplation of what I observed while the engine was apart, and what seems to happen like clockwork with the full load testing, I can come to only one conclusion: The engine part that gets the hottest is where the problem must lie - the exhaust valve. I say this for a few reasons:

While the engine was apart, the top of the combustion chamber had carbon deposits, the piston had carbon, the intake valve had carbon, but the exhaust valve had ZERO carbon. This is not totally out of the ordinary, but this indicates that all the other parts were much cooler. My assessment based upon the color of the metal of the exhaust valve was that it could have been overheating.
 I didn't do the felt pen trick to accurately assess the valve face/seat contact point, but after careful cleaning with carbon solvent only (combustion chamber cleaner) and a toothbrush (no abrasives), I could clearly see the line on the intake valve face which was right down the middle. The exhaust valve had no line and the wear mark was clearly not in the middle.
I opted not to relap either valve with the grinding compound and rubber hose method. The intake valve did seat slightly lower after carbon cleaning since I did have to slightly increase the rocker arm clearance at the top; I was encouraged by that. The exhaust valve had no deposits at all, so its rocker arm clearance didn't even change by 0.001".
While the cylinder was upside down with the valves closed, I soaked it in the combustion chamber cleaner for several hours, multiple times. The intake valve never leaked through to the intake manifold, but the exhaust valve did very slightly leak cleaner fluid into the exhaust manifold.
The compression test done after reassembly showed NO CHANGE from previous tests. I did not rerun a leakdown test since it had been so stellar before the teardown.

My logic may be flawed, but the symptoms during full load testing are just too indicative - IMO - that something is getting hot, causing a power loss, and then being relieved by throttling back for a minute or two, allowing it to recover to attain full power (5000RPM) for a shorter period of time again, before the same degradation happens again. Obviously engine parts with a lot of mass (e.g. cylinder wall and everything attached to it) are not going to cool off that quickly, but the exhaust valve will vary in temperature quite a bit as RPM drops, the seated time duration increases, and the heat applied due to lower-throttle combustion decreases.

*The Plan of Attack - barring natural disasters*
The exhaust valve is ordered and we'll tear 'er apart again next weekend - unless Hurricane Irma decides to change my plans here in SE Florida - in which case the generator will stay as is for emergency use!

*Some side notes about Engine Cleaning Products*
Along the way of doing this teardown, I had to do a lot of research and obtain some specialty cleaning products that I wanted to share my experience with to perhaps help someone else. They consisted of the following:


Gunk Engine Parts Cleaner & Degreaser - This is basically Acetone and Heptanes in a CO2 aerosal. I had a can of Acetone, but having the convenience of a spray can for final parts rinsing was nice. 
CRC Brakleen - This is some caustic stuff as everyone already knows, and I bought it for one specific purpose - to clean off the old Honda Bond 4 gasket maker. After trying ever other chemical I could find, this stuff did the trick. I was very careful to keep it away from any plastics or rubber parts.
Mopar Combustion Chamber Cleaner - This stuff turned out to be less miraculous than what I saw in an online video where totally dirty parts came out like new, but I think it is some of the best stuff available. I also think EasyOff Oven cleaner might have also worked! Basically, this stuff is carbon deposit remover. I wanted to use a chemical method rather than wiring brushing the top of the combustion chamber (remember the Honda EU2000i has no removable engine head). It also allowed me to clean up the valves and the piston without risk of scratching. I rigged up a special toothbrush and baked some of the metal components to 250°F in the oven to help loosen the carbon further. It was painstaking and took a couple days, but I got everything to where I was satisfied.

I've attached a bunch of photos below. I'll post again once I get through the next chapter in this saga!


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## AstroBruce

Matteo, Have you tried giving the exhaust valve a tad more lash? With all the heat, it might be unseating itself.

AstroBruce


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## thehandyman1957

Looking at that picture of your cleaned valve seats I wonder if the discoloration on the left side of your exhaust valve is a tell tale sign of excess heat. Also, when seeing that line on your exhaust valve makes me wonder if that is all the seating your getting with that valve. 

I would make sure the valve seat is ok, and perhaps have the seat lapped with your new valve. With all that work, it's not worth it to put it all back together again just to find out the seat is having issues. 

On a side note. When I tore apart my LP66 Primepact generator, I had the same leakage issue in my exhaust valve and after doing my own lapping, stopped it from any leakage. Ran like a champ. 

Sorry to hear about your long battle with this little unit. I also wish you the best luck with Erma.


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## Micro-Air

AstroBruce said:


> Matteo, Have you tried giving the exhaust valve a tad more lash? With all the heat, it might be unseating itself.


Hi (again) AstroBruce! Yes. In fact, I did a bunch of tests early on where I purposely over gapped the exhaust valve clearance to see if it would have any effect. It did not.



thehandyman1957 said:


> Looking at that picture of your cleaned valve seats I wonder if the discoloration on the left side of your exhaust valve is a tell tale sign of excess heat. Also, when seeing that line on your exhaust valve makes me wonder if that is all the seating your getting with that valve.
> 
> I would make sure the valve seat is ok, and perhaps have the seat lapped with your new valve. With all that work, it's not worth it to put it all back together again just to find out the seat is having issues.
> 
> On a side note. When I tore apart my LP66 Primepact generator, I had the same leakage issue in my exhaust valve and after doing my own lapping, stopped it from any leakage. Ran like a champ.
> 
> Sorry to hear about your long battle with this little unit. I also wish you the best luck with Erma.


Thanks, Handyman. I agree with you. I've done some reading elsewhere and there appears to be a couple schools of thought on the lapping of a brand new valve. Some say yes and some say no. I tend to agree with you though that lapping with the new valve to ensure the seat is okay and well matched/mated is probably the right thing to do. I'd rather lap with the new valve in case the old one is in fact warped (as I am hoping). I am going to use the dry erase marker method to evaluate the interface. As long as I don't have to "recondition" the valve seat, I'll be happy. Lapping is much easier. Reconditioning requires special grinding tools and I would be a bit shy about potentially irreversible mistakes. Since the seat is well cooled, and I took a very close look at it under magnification several times with the valve uninstalled, I believe it is okay. As you found in your experience (thanks for sharing it), I believe the exhaust valve and its seating once at higher operating temperature is the culprit. Also, one could rationalize a bit of a runaway effect going on here too: Once the valve is no longer seating, not only is the compression lower, but the mixture will become leaner since more (dirty) air can come in through the unsealed exhaust valve rather the fresh air through the intake, which brings with it the appropriate and proportional amount of fuel. Leaner mixtures cause the engine to run hotter as we discussed earlier. So, once the exhaust valve starts to lose its seating due to "normal" heating at full throttle, the problem just snowballs from there.

Hopefully the new exhaust valve arrives before Irma, and Irma decides to be the "fish storm" we'd all prefer. Right now though, it's not looking too good for us here in south Florida. Needless to say, today during the holiday I put the side panels back onto and gassed up the Honda as it stands. I may need it, for the mere 13-14A it can provide without this power loss problem!


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## Nixamousa

I have two of this little Honda's and have not had any problems with them. As a former small engine tech your post caught my eye. You are doing the right things, a process of elimination. From your description and solutions attempted it is possible that you have a damaged crankshaft bearing & journal, perhaps the flywheel side or PTO side bearing. It is not likely the rod journel as it would also likely knock. Since I have not disassembled one of these engines I do not know if they use needle roller bearings, bronze bushings or a combination. But in other small engines that I have worked on the description you provide fits. If there is a damaged bearing or journal once it heats the engine begins to warm, friction increases, the engine can "bind" and the rpm can slow or even stop. The cause is usually lack of lubrication due to low oil (or no oil) in the crankcase at one time or another. Unfortunately, no way to know until complete disassembly. But in my experience, if this is the case the engine will not be salvageable. Just another experience to add to your detective case.


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## Micro-Air

Nixamousa said:


> I have two of this little Honda's and have not had any problems with them. As a former small engine tech your post caught my eye. You are doing the right things, a process of elimination. From your description and solutions attempted it is possible that you have a damaged crankshaft bearing & journal, perhaps the flywheel side or PTO side bearing. It is not likely the rod journel as it would also likely knock. Since I have not disassembled one of these engines I do not know if they use needle roller bearings, bronze bushings or a combination. But in other small engines that I have worked on the description you provide fits. If there is a damaged bearing or journal once it heats the engine begins to warm, friction increases, the engine can "bind" and the rpm can slow or even stop. The cause is usually lack of lubrication due to low oil (or no oil) in the crankcase at one time or another. Unfortunately, no way to know until complete disassembly. But in my experience, if this is the case the engine will not be salvageable. Just another experience to add to your detective case.


Thank you for the compliment, Nixamousa. Your point is a valid one and I did briefly contemplate such a possibility as a cause of the drop in RPM, rather than it being due to motor power output reduction. After disassembling the motor though, I discarded this possibility. Here's why. 

If you examine some of the photos in my previous posts, you can see the Honda EU2000i's crankshaft bearings. Unlike most small engines which have shaft bearings like you described, the Honda EU2000i's are very high quality and large ball bearings! Yet another component and design feature of the Honda that I found quite impressive. The bearings and the interfaces to the crankshaft are quite unique, ultra durable, and not at all prone to any sort of alignment issues or binding. For the ball bearing on the power output side of the crankshaft, the inner race is press fit onto the shaft, and the outer race is a slip fit in the crankcase/cylinder portion. For the ball bearing on the butt end of the crankshaft that stays internal, the inner race is a slip fit on the shaft end, and the outer race is a press fit into the crankcase cover. If you were to look at it first hand, you would also likely agree that there is very little likelihood of warping or interference that could cause the shaft to to suddenly bind or have an increase in friction, even if it shifted or expanded a bit over temperature. The crankshaft itself looks like it belongs in a motor twice the size. Both bearings looked pretty much brand new in my opinion. Quite amazing for an 8-year-old generator.

ACTIVITY UPDATE: The exhaust valve is shipping today as expected, and I picked up some valve lapping compound and some other items so I am prepared to do the next iteration by the weekend. Of course, if Irma decides to come within 50 miles, I'll likely be using the generator as is!


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## Nixamousa

I admire your pursuit and hope you find the problem. I once had a newer lawnboy engine in the shop and neither I nor the factory tech could find the problem. What I learned from the experience is time is valuable and at some point you just say it is time to move on. I will be following and if you do find the issue please post your findings.


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## Predator

Micro-Air,
Have you tested the resistance values of the ignition coil?
Honda EU2000i Ignition Coil - Fits EU2000i inverter generator 30500-z07-023 | eBay

If it's faulty, it can present the symptoms you are dealing with.

I have one of these so I'm following this thread.


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## Predator

Oh...I was going to add that this wouldn't affect compression, however.

(I'm not yet able to edit my own posts)


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## Micro-Air

Predator said:


> Micro-Air,
> Have you tested the resistance values of the ignition coil?
> If it's faulty, it can present the symptoms you are dealing with.
> I have one of these so I'm following this thread.


Hello Predator. Thank you for the idea. Yes, I did measure both the primary and secondary sides, and they were within the specifications shown in the service manual (0.7-1.1 ohm primary; 12k-21kohm secondary). Also, one would expect that any sort of intermittent, temperature-related failure in the ignition coil should result in symptoms of misses in the ignition/spark during the high-load condition when the RPM begins to drop. Having very closely monitored the engine behavior during said conditions, I witnessed no evidence or symptoms to support the possibility that the spark was behind the RPM reduction. Nevertheless, your suggestion is a key part of the "fuel, spark, air, compression" process of elimination. 

As a further update for everyone, I did end up using the Honda for 5 days after Hurricane Irma knocked out power. The recovery is still ongoing since we did have damage and lots of cleanup, in spite of being 100 miles from the center of the storm (thankfully it wasn't 0 miles as originally predicted!). The Honda ran find of course for loads under 1500W. I have the new exhaust valve in my possession, and all of the other items I will need for the next step in the process. I'm out of town on business this week, so I won't be able to get back to working on this project until this coming weekend. I'll keep everyone posted.


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## Predator

Since I have one of these EU2000is and I do a lot of engine work, this thread is a treasure. Especially with all the photos.
Since it's all back together, I'd be curious to do some thermal readings with a laser thermometer and compare those against others who have the same unit.

I'd be glad to supply such readings if you go that way.
You have ruled out the inverter as the source of the problem....and now the engine for all intents and purposes. So what's left?

It is still possible you have a more difficult to diagnose engine problem such as a valve guide that is moving under heat, a hard to find crack in the head.....etc
These are the "not so obvious" issues that any internal combustion engine "can" suffer. It could be a manufacturing casting flaw for example.

Your compression readings still concern me. I work on a LOT of small engines.....scooter engines....49cc - 150cc engines. Let me say from experience that these engines begin to faulter under 70psi compression. I can get them to run at 65-70psi, but they aren't able to make any power. In fact, all of the engines mentioned above are happiest at around 150psi.

Now, when I take compression readings on these engines, it's imperative that the throttle is WIDE OPEN. A closed throttle will give a significantly lower reading because it effectively blocks the incoming air and created a vacuum.
So it makes me question, does Honda specify whether the throttle plate should be wide open or closed during these tests?
I also find that compression is generally higher with a hot engine than a cold engine so that somewhat goes against your findings of it running worse after 3 - 4 minutes.

I'm going to check the compression on mine out of curiosity. It's running perfectly. I'll post the answer as soon as I do.

Perhaps there is simply a fuel delivery issue. Have you replaced ALL the fuel and vacuum lines? I've seen some ridiculously small leaks cause serious problems.

The fact that it waits until the engine has run 3-4 minutes would indicate some sort of overheating issue...but it could also indicate a fuel starvation issue.

Like I said, I would get the temp of some point on the exhaust where you can accurately measure it against several other Honda EU2000is and see if it run hot.
I would also check points on the Rotor/stator and anywhere else you might find a good reference. High heat points compared to other identical generators could lead you to the issue. Sometimes I wish I had an FLIR camera for stuff like this.

Think about the 3-4 minute time frame.....what dynamic processes could cause this? How much fuel is in the lines between the tank and fuel valve and carb?
Is it enough to keep the genset running at full power until the reduced flow can no longer keep up? What about vacuum in the gas tank? I have seen defective gas caps that would not vent cause a vacuum in the gas tank and reduce fuel flow after several minutes. 

Just some thoughts if you haven't found the definitive answer yet.


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## Micro-Air

Thank you for your input, Predator. Most of your questions have already been answered in previous posts in this thread. But some have not, so I'll go through it briefly.

Exhaust Temperature
Using a Fluke Laser reader, at full load (2000W) the temperature of the exhaust was up at around 450°F for the bad Honda and perhaps 100°F cooler with a good Honda. How accurate this is I cannot tell, but data seems to indicate that the bad Honda does run hotter just before and during the drop in RPM. 

Compression Test
This was covered in the first post, and also in later posts with some leakdown tests as well. Honda specifies 71PSI for this motor, and they do not specify what the throttle setting should be for the test. Even after the piston ring replacement, the compression for the problem Honda is still about 10PSI lower than two separate "good" Honda EU200i generators. All tests were done with the default engine-off throttle setting, which is closed. 

Fuel Delivery
In an effort to avoid any questions or doubts, as mentioned in previous posts, early in the investigation all of the fuel system components were replaced with brand new OEM versions: carburetor, fuel filter, fuel pump. Fuel and vacuum lines have been meticulously inspected and tested under pressure. They're pristine and do not have any leaks. Although fuel delivery isn't the direct cause, I believe it is _indirectly_ affected during the actual issue; more on this below.

Gas Cap
As was covered in a previous post, this was eliminated by removal of the gas cap during a test iteration.

3-4 Minute Behavior
The behavior of the generator and the gradual, consistent drop in RPM at verified full throttle is not only very repeatable, but also reversible by short runs (~1 minute) at low RPM, allowing whatever has overheated to somewhat cool off. After these brief low RPM runs, the generator can once again attain 5000RPM, but for less time than the original 3-4 minutes. This very consistent behavior is more indicative of a high-temperature, high-load induced anomaly. Fuel starvation due to a problem in the fuel system itself is unlikely as a result. However, this is not to say that the fuel _mixture_ isn't exacerbating the problem. In fact, a "runaway effect" is likely taking place. Once the exhaust valve heats to the point where its warpage causes reduced seating alignment, the valve will dissipate even less heat during its already very short seat time, further worsening its overall condition. Combine this with air leakage through the exhaust valve during subsequent intake strokes and that results in less air coming through the intake valve, thus drawing in less fuel due to the proportionally reduced air flow through the carburetor where it is supposed to be coming from. Less fuel for the same amount air results in a leaner mixture, which of course causes increased heat generation during combustion. That in turn further aggravates the condition on the exhaust valve in subsequent power and exhaust strokes. Remove the load and throttle back, and things recover quite quickly as the localized (e.g. valve) temperature drops from extreme highs of several hundreds of degrees, down by a substantial percentage, thus resulting in less warpage, slightly better seating, once again allowing full RPM and sufficient performance upon application of full load and full throttle, albeit very brief.

------------------------------------

Of course, all of the above is yet to be proven, but the extensive testing and all of the gathered observations, data, and evidence are all pointing to a phenomenon such as this. Exhaust valve problems like this are not an uncommon form of engine performance loss. Certainly, it's uncommon in the Honda EU2000i (!), but based upon the reports we have been receiving from our large customer base across a very large population of Honda EU2000i (>1000 units), we believe it may be occurring in a very small handful of cases. Thus the reason we bought this generator from one of our customers and why I'm taking this investigation to a firm conclusion, regardless of the monetary or time cost. 

I've been traveling on business for the past week, working 7 days for the past several weeks, so I haven't been able to disassemble the engine again quite yet. I'm optimistic a window of opportunity will open during this coming week. I'll post here as soon as I have test results.


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## Predator

FYI.....

I ran a compression test on my EU2000i tonight
Engine totally cold

31psi is the best I could get.
That said, I've had no problems with mine. I just used it after hurricane Irma and it performed as expected (as best I can recall)

I'm a bit surprised at this compression as I honestly expected much higher...closer to the maximum. Reason being is that mine has been cared for like an aircraft, gently used, always stored under climate controlled conditions, oil changed religiously and it probably has relatively low run time compared to the average EU2000i. I would say it's had a very easy life.
I'm actually now questioning my compression tester because I would expect some difficulty getting it started at very low compression values and yet it starts right up....seems to run fine and I've never heard it skip a beat.

But to be honest, I haven't sat with it for long enough to actually notice an RPM / Voltage drop because I have never been concerned about it. I've always started it then gone about my business trusting it was doing it's thing. Now that I know my compression is down where Ron's is, I'm going to do a lot more investigating.

Now I'm curious and will run it under the conditions you described in the OP and I'll be paying strict attention for any reduction in RPM at the 2-6 minute mark.

*Enter the problem generator owned by one of our customers. His name is Ron. Ron's generator will start off providing the full load amperage up to the 16.7A limit (say 16A for sake of testing), and its motor will reach and stabilize at the 5000RPM like all of the other Honda generators under the same test condition. Then, after about 3 to 4 minutes of operation, Ron's generator will start dropping in RPM. I know the throttle and its associated motor servo very well since we replaced Ron's carburetor with a brand new one a few weeks ago when this all started. The THROTTLE IS WIDE OPEN AND UP AGAINST ITS STOP for the entire time this RPM reductions starts and continues to take place. So, we know its not a control system issue. Ron's generator will then slowly drop in RPM, going as low as about 4400 RPM, and if the load is kept on, the output voltage of course will also start dropping. At no time is the load brought above the 2000VA limit (16.7A), so the generator never declares an overload (lights its LED). The voltage will eventually drop to about 98V if I keep the load up at about 15A. I don't have a precise load bank device, so my ability to adjust the load precisely as the voltage drops gets difficult since the load devices I'm using draw less current as the voltage drops.
*


If for any reason mine has a similar problem, it would probably be my last Honda generator since I have several other non-Honda generators that were MUCH less expensive that are still doing fine after much more run time.

My curiosity is piqued.

*UPDATE:*
Doubting my compression tester (one of them, I have many) I went and tested the compression with a different compression tester and got much different results....

*60psi*

I really want to believe that the real compression is 60psi because it runs so good and that makes MUCH more sense given the history of it.
Nevertheless, I'm going to check it for any RPM drop just as you did. Will report back as soon as I do.

(I'll sleep better with that 60psi reading)


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## Micro-Air

Predator: Your compression test results don't surprise me. The "good" Honda EU2000i generators I tested had about 45-50PSI and the problem Honda had about 35-40PSI. Upon further checking their service manual, the 71 PSI spec is stated in two places. In one place, they also specify an RPM at which it is supposed to be measured, which is 700RPM. I doubt any of us could produce that much RPM using the recoil starter alone. One of the 2 good Honda's I tested was close to brand new, so 50PSI looks like the max I could get. Since the tests were conducted the same way for all of them (i.e. I pulled on the recoil start as sharply and as fast as I could), the relative measurement results are still likely valid. That is, the problem Honda has about 20% less compression than the good Hondas.

Also, on minor correction to what I wrote in yesterday's reply: Upon re-disassembly, I just looked inside the carburetor and found that the throttle is wide open if the off state, not closed like I originally stated.


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## Predator

If the throttle plate is wide open normally (unlike motorcycles or cars etc), that would make more sense for the compression test as normally it is performed with the throttle plate wide open and as many small engines as I build, custom build and rebuild, I've found it makes more difference on smaller engines than larger displacement ones.

Also, compression tends to be higher once the engine warms up in most engines. The piston is of a softer metal and tends to expand more than the cylinder around it.
All by design. I would expect 70psi on mine warmed up and tested. Testing compression cold is not really "standard". It's most often recommended to test compression with the engine warmed up. Does Honda specifically say to test this generator's compression "cold" or does it just list the "cold" compression value?

With all you've already tested, it seems you have a guide issue, a valve seat issue or a small crack in the head somewhere.

All I can say is,.....I'm glad I don't have this issue

Oh...and never trust just one compression tester


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## Micro-Air

*Round 2 Disassembly/Reassembly Finally Underway*

UPDATE:
I just wanted to let everyone know that I spent Tuesday tearing down the Honda for the second time, I did the valve seating tests with the dry erase marker, and I did the valve lapping of both the original intake valve (not replaced) and the new exhaust valve (replaced). I've spotted wear and a distinct ridge on the exhaust valve, and the wide black band that was there does appear to be the where the seat was occurring. This black band is very wide indeed, much wider than the seat, so that was peculiar to me. Unfortunately, the black marker test didn't reveal precisely where the seat was happening on the old exhaust valve, probably because it wasn't consistent! The new exhaust valve - after lapping - has a clear seating point that is as wide as the seat itself and close enough to the middle to avoid having to recondition (re-angle) the valve seats. Same is true for the intake valve. I included the old exhaust valve in some of the attached photos for comparison purposes. The last photo is a blowup of the exhaust valves where you can see some concave and a bit of a ridge on the old valve, versus the consistent slope of the new valve.

In general, I must say that the act of lapping the valves with valve grinding compound is a unnerving and seemingly harsh process! Valve grinding compound is some serious stuff. It certainly removed material from both the seat and the valves. They recommend watering it down for a second lapping step where you smooth out the results of the first lapping step. I couldn't seem to get the grit down to a level I liked, so I used some other rubbing compound paste for the "finishing" lap, which seemed to work nicely. I ended up using the rubber hose and slow-speed drill rotation method, versus the suction cup method because I liked the results I saw in multiple articles and YouTube videos that used the drill method. Bottom line, both valves are seating magnificently now, and I don't think it could be much better. Obviously, we're most concerned about the exhaust valve since that is likely where the problem lies at high temperature. Yes, I did completely remove any remaining lapping compound and the cylinder casting is squeaky clean now, ready for reassembly. I even already did the steps to remove the old HondaBond 4 gasket maker from all the parts, which was as time-consuming as it was the first time. The good news was that my application of the HondaBond, visible after the teardown, indicated that I did a good job in my first reassembly. There's nothing better than doing a second teardown to critique your own work! 

Over the next day or two, I will be doing the reassembly, barring other work-related disasters that keep me from it. I'm going to video tape the reassembly for a possible future video on our company's YouTube channel, since I don't see any full teardown or reassembly of a Honda EU2000i down to the last engine component anywhere on YouTube (only partial steps). What I've ventured into here may be useful to others, so that's my motivation.

After that, will come the pivotal load test again. Fingers crossed....


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## Predator

Lot's of work!

I do so many valve lapping jobs on motorcycles and scooters I can't count them anymore.

To test your work before re-assembly here's what you do.....

You'll need a compressor.

Hold the head so that the head gasket surface is horizontal. Fill the valve and combustion area with water so that it completely covers the valves.
Now, using an air gun on your compressor, blast air into the exhaust port, and then the intake port...gradually (you don't want to blow the valve open)

When you have a really good seal, you'll see no air bubbles coming past the valves. 

Really enjoying this thread. Someday I'll be rebuilding my little Honda I'm sure.

You did a good job cleaning up that head <thumb-up>


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## Micro-Air

*UPDATE: Exhaust Valve replacement did NOT resolve the issue*

Great disappointment here.  In spite of the efforts, a smooth reassembly and easy startup today, the RPM loss after a few minutes of full-load operation still persists, pretty much identically. I'm now at a loss as to what is going on, so I'm going to have to sit back and think about it. New piston rings, a new exhaust valve, and a relapped intake valve should have had an effect if compression loss at high temp was the cause. Also, every component in the fuel system was previously replaced months ago with brand new OEM parts, and that had no effect either. I'm obviously barking up the wrong tree, so I'll have to take a fresh look and consider the causes that were previously analyzed and eliminated. Too much time has already been invested to give up now. Worst case, I'll have to buy a second Honda EU2000i that passes the sustained load test and start swapping parts to narrow in on the root cause.

I'm heading out of town on business again tomorrow, so I'll post again once I have a plan after I return. I'll appreciate any other thoughts or ideas in the meantime.


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## Predator

Micro-Air said:


> Great disappointment here.  In spite of the efforts, a smooth reassembly and easy startup today, the RPM loss after a few minutes of full-load operation still persists, pretty much identically. I'm now at a loss as to what is going on, so I'm going to have to sit back and think about it. New piston rings, a new exhaust valve, and a relapped intake valve should have had an effect if compression loss at high temp was the cause. Also, every component in the fuel system was previously replaced months ago with brand new OEM parts, and that had no effect either. I'm obviously barking up the wrong tree, so I'll have to take a fresh look and consider the causes that were previously analyzed and eliminated. Too much time has already been invested to give up now. Worst case, I'll have to buy a second Honda EU2000i that passes the sustained load test and start swapping parts to narrow in on the root cause.
> 
> I'm heading out of town on business again tomorrow, so I'll post again once I have a plan after I return. I'll appreciate any other thoughts or ideas in the meantime.


Sorry to hear this micro.
Did you re-check the compression?

Since the compression was low to begin with, if you still have low compression then you still have a problem somewhere in the head or piston.
You'll never get anywhere until you resolve the compression issue.

Do you have access to an Exhaust Gas Analyzer? That might help narrow down the cause.
Maybe take the generator to a local shop that has one and will do an analysis for you.

I've seen some weird stuff having worked on so many engines. I've seen mufflers that came apart inside and once hot, restricted flow.
I've seen intake elbows get soft after the engine warms up and collapse from the vacuum. etc etc.

Maybe the low oil sensing circuit is bad and goes into high resistance once hot and is grounding off some of the ignition current but not all? Try disconnecting it.

But you must completely rule out a compression problem first.


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## Micro-Air

UPDATE: I've been very busy with other work, so I hadn't had an opportunity to try the next parts replacement. After discussing the problem with some other small engine experts over a month ago, they suggested replacing the valve springs since power loss at high-RPM and high-temperatures could be explained by this. I had ordered the parts many weeks ago and already them. Today, I was able to carry out the replacements, but it did not resolve the problem during full-load testing. Engine compression is now almost completely eliminated as a possible cause.

In the processing of doing the testing today, I observed some peculiar ignition behavior via the RPM meter that now has me wondering if the perhaps the problem is spark timing related. The ignition module does have a rev limiter algorithm built into it, so it is possible that it could be malfunctioning somehow. I'm going to replace both the ignition module and coil next to eliminate them as a possible causes.


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## KRE

Check your engine timing, as timing off spec will cause a engine to overheat. Also check valve clearance as re-seat time being off can also cause a engine to run hot at full load, but not normally at off peak load. 
A higher than normal engine temp, will cause the fuel to expand an you loose fuel BTU content at that point. Also if the engine is running lean it will run hotter than normal.
It will be something simple, trust me. Could be as simple as a wrong heat range spark plug, to a fuel line being improperly located into a high heat area, or a slightly restricted muffler. Any one of those will not cause a problem most will detect until you get to full load an try to maintain same for awhile. It matters little if it is a single cylinder, or 20 of them the basics are the same. 

Hope this helps,
Kenneth


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## Handyhiker

I must admit I did not read all of the posts but I did not see where you ever tried a different fuel supply tank. With the 3 minute run time that is about what it takes to run the fuel bowl low. Hook up a different tank and plug the new tank line in the fuel pump to bypass the problem generator fuel system. My bet is a bad fuel **** ot a plugged tube in the tank. If your boss worked on motorcycles I am sure he has a fuel tank that hangs with a hook so you can run a motorcycle engine with the tank removed. It just sounds like fuel starvation with the hotrer exhaust and rpm loss. 
I do not know for sure, but could you just stick a fuel hose in a can and the other end to the pump?


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## Handyhiker

Guess you can't say fuel c,o,c,k on here.


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## Predator

Also, it's very often something that you checked, and assured yourself that it was ok....because it "passed" your tests but in fact was actually defective all the time. Even brand new parts.

Recently had a spark plug cable do that. Passed every test I could throw at it and met and exceeded OEM specs.

But alas....ultimately IT was the problem.

Hint: NEW parts can be defective.


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## Micro-Air

Handyhiker said:


> I must admit I did not read all of the posts but I did not see where you ever tried a different fuel supply tank. With the 3 minute run time that is about what it takes to run the fuel bowl low. Hook up a different tank and plug the new tank line in the fuel pump to bypass the problem generator fuel system. My bet is a bad fuel **** ot a plugged tube in the tank. If your boss worked on motorcycles I am sure he has a fuel tank that hangs with a hook so you can run a motorcycle engine with the tank removed. It just sounds like fuel starvation with the hotrer exhaust and rpm loss.
> I do not know for sure, but could you just stick a fuel hose in a can and the other end to the pump?


Thank you for the suggestion, Handyhiker. Thinking along the same line of logic you cited about the time to empty a fuel bowl, about 3 months into this saga (we're now in month 5), in order to eliminate fuel delivery to the brand new carburetor as a cause, I removed the fuel tank, flushed it out and cleaned it thoroughly, temporarily removed its inserted fuel filter, added some separate fuel line that was longer that bypassed the fuel petcock and fuel pump and went straight to the carburetor fuel bowl inlet, added fresh fuel, and then placed the fuel tank about 3ft above the carburetor for a true gravity feed. During the pivotal test, the 3-minute power-loss problem was unaffected.



Predator said:


> Also, it's very often something that you checked, and assured yourself that it was ok....because it "passed" your tests but in fact was actually defective all the time. Even brand new parts. Recently had a spark plug cable do that. Passed every test I could throw at it and met and exceeded OEM specs. But alas....ultimately IT was the problem. Hint: NEW parts can be defective.


I'm beginning to wonder the same thing, Predator. Admittedly, I feel like I'm starting to circle back around, but at least I now feel very confident in the engine compression and engine aspects of what is going on are now safely eliminated. I also did enjoy the learning I gained doing the drudgery of 2 full disassembly & reassembly processes.


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## Predator

Micro-Air,
This is one of those situations that is a mechanics nightmare. I've run into them.

I commend your tenacity and the fact that you won;t give up on this. I'm finding this thread to be a nail biter and really want to know what the final outcome is.
There have been some very good recommendations in this thread.

Because I ran into something like this recently have you tried the really simple stuff....ie have you swapped out the ignition coil and spark plug cable just to make certain those were ruled out? (You may have but I'd have to re-read the entire thread)

Someone said they'd bet it was something simple and I have a feeling that is correct. Something so simple it simply gets over looked. Maybe something you checked that passed "the test", but it is still the problem?

I I had that generator, I would try to nail down whether it is a fuel delivery issue or an electrical issue. My bets are still on an electrical issue. I find it amazing that the compression was so low initially, and you corrected that, and still have the problem. As mechanics, we tend to like finding an issue and hoping that it IS the solution.

Have you tried MANUALLY adding fuel into the intake stream when this condition starts (just to reinforce that it's NOT the fuel system)?

Have you put an inductive timing light on it to check the timing under full load?

What is the temperature at the exhaust outlet several minutes AFTER the rpms start dropping? Is it running unusually hot?

Could it have a partially blocked spark arrester or a muffler problem that's causing a restriction in flow (temp check would reveal).

What is the compression now that you've done all the cylinder /valve/rings work?

Could the oil pump be having an issue and oil flow is reducing when hot partially triggering the Oil Cut off switch?


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## Marlin

I just found this site last evening, November 12, 2017, and I did read every entry, word for word. I kept waiting and looking for two things, but they never happened.

First, I was waiting for someone to point out that the Honda EU2000 does, indeed, have a compression release mechanism.

There are those who will argue with that, because they do not see it and it is not specifically pointed out in the parts list. But, it is there and will give a false low compression test reading.

If you look at the lobe side of the cam sprocket, you will see a spring loaded device that interferes with the valves until the RPM gets up high enough for centrifugal force to pull it away.

I have read that to do a compression test on one of these engines, the engine must be turned backwards, which is not possible with the recoil starter in place.

The other thing I was waiting for was to see someone make a suggestion about how to check and see if the generator is running with too lean of a mixture from the carburetor.

The suggestion is to remove the filter in the air cleaner and leave the front cover of the air cleaner off, and start the engine and put it under the typical load where it begins to fail.

Then take a standard and typical propane torch, but do not light it, and hold the tip up next to the inlet of the carb and let some propane enter the air stream where the air goes into the carb.

If the increase in incoming fuel causes the engine to slow down and sputter, then the original mixture was probably fine.

But, if by chance, the engine speeds up a little, then the additional fuel is showing you that the original mixture was a little too lean.

That test is easy, simple, and costs next to nothing but a little time.

Hopefully, we will soon see another entry here giving us the final results of your investigation, we can hardly wait.


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## Predator

Good points.

I searched this entire thread and MicroAir (and noone else) ever mentioned a compression release. I would think he'd know about it as his company repairs them. Noone else did either that I could find so you may be on to something.
I'm an experienced engine mechanic but have not yet torn into one of these eu2000i's. But I have one.

Youtube Video Honda eu2000i Compression Release


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## Scottbeef

Have you tried running it without any muffler? I am not mechanical in the least. But I had that exact same unit dropped off to me non working. My dad had it into a Honda dealership they cleaned carb, put in a new spark plug, and adjusted the valves. Still no luck. They told my dad it was a bad control box ( inverter box). For no apparent reason I wanted to check if my dad ever removed the spark arrester. He had not. Thought ok whatever why not try starting it without the muffler in case the spark arrester was plugged. Started right up! As soon as I tightened muffler back up it died. Removed said arrester all together. Same result. As s soon as muffler was tightened down it died. Nobody close by had a muffler in stock and they run $140. So I thought I would try opening up the muffler. No luck blowing compressed air thru it. Ended up simply putting a Flathead screwdriver into the muffler output and enlarging that hole inside. Reattached muffler started right up. Not a bit louder then previously and running great. To do it right I should clean up the spark arrester and buy a factory muffler.


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## Predator

Scottbeef said:


> Have you tried running it without any muffler? I am not mechanical in the least. But I had that exact same unit dropped off to me non working. My dad had it into a Honda dealership they cleaned carb, put in a new spark plug, and adjusted the valves. Still no luck. They told my dad it was a bad control box ( inverter box). For no apparent reason I wanted to check if my dad ever removed the spark arrester. He had not. Thought ok whatever why not try starting it without the muffler in case the spark arrester was plugged. Started right up! As soon as I tightened muffler back up it died. Removed said arrester all together. Same result. As s soon as muffler was tightened down it died. Nobody close by had a muffler in stock and they run $140. So I thought I would try opening up the muffler. No luck blowing compressed air thru it. Ended up simply putting a Flathead screwdriver into the muffler output and enlarging that hole inside. Reattached muffler started right up. Not a bit louder then previously and running great. To do it right I should clean up the spark arrester and buy a factory muffler.


See post 14

He removed the spark arrester with no change. But he never removed the muffler on account of disturbing the neighbors.
You could have used SeaFoam to clean the inside of that muffler. High heat will also clean out a clogged muffler in some cases as long as you don't damage it. Mainly small engine mufflers without fiberglass packing.


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## Predator

MicroAir hasn't been heard from in this thread since the end of October.

It's a same if we don't know what became of this....or if he just gave up.

Calling MicroAir.....


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## Micro-Air

Predator said:


> Youtube Video Honda eu2000i Compression Release


Hello everyone. Sorry I was not responsive to the most recent replies. For some reason, this forum doesn't always alert me (via e-mail) to new replies in this post, even though I have confirmed over and over that I am subscribed. The e-mail alerts seems to work for a few weeks after a reply by me (or a deliberate unsubscribe/resubscribe) but it quits sending me e-mails after a while.

In any event, Predator, thanks for the video a few replies back. I am aware of the compression release lever on the cam pulley, and it only affects start-up (extremely low) RPM. Once the motor is up and running, the lever flies to its outward position, thus retracting the metal piece that holds open the exhaust valve, as the video explains.

I have done one more set of experiments since my last update. I replaced both the spark control module and the ignition coil, even though I had no reason to suspect either. My only thought was a possible flaw in the rev limiter, which is done in the spark controller. Neither change had any affect on the problem. 

During the testing though, since the weather is cooler, even here in Florida, the sequence of events that occurred during the 3-5 minutes of proper full-power operation changed a bit. I will document the symptoms at another time, but I'm pretty much to a point now where I'm going to have to verify that the normal full-power heat-up of the stator windings, rotor magnets, and inverter module are not causing the breakdown. Those are the only items left that have not been replaced. The only way to prove this is to swap each item one at a time with those from a known-good generator. The cost of these items is too much for me to handle with personal funds (which I have been using this entire time since May), but I do have access to a business colleagues Honda EU2000i that I know passes the sustained (long-duration) load test that my generator does not. This swap testing may not happen until early next year, but that is the ultimate plan. If I drop out of communication, please do not be disturbed. I'll be back with updates eventually. Thank you again for everyone's ideas and input.


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## thehandyman1957

Glad to hear from you again Micro-air. Sorry you have not been able to find the solution yet. I do hope you eventually figure this out.
If anything, just to simply know. I'm sure there will be someone out there that may run into this problem and not have the money or the time to figure this out. We will be waiting for your next update.


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## Micro-Air

QUICK UPDATE: I finally got around to replacing the inverter module with a brand new one, and the problem was not resolved. I will be replacing the stator next since I now suspect stator heating is causing one of its windings to leak and/or short. Hi-pot (megohm) and oscilloscope readings are indicating that this may be the root cause of the drop in output and increase in engine load after 3-5 minutes of full power operation (and stator heating).


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## thehandyman1957

Wow, your going to have a brand new gen set pretty soon. Might as well get a new case when you finally figure this all out so it looks as good as it runs. : )


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## Sriganesh

Hi Matteo Giovanetti, An Interesting post thanks to sharing such a valuable information. 

*Advertisements removed from post.* I hope your post will defiantly educate lot of thing in the generator industry thanks again.


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## Tonyrevis

Man out just put a ptromerter and 5 gas Analyzer on it a cheap one will work fine my best guess is exhaust temp will rise and it will lean out for one of 2 reasons. A vacuum leak that shows as the temp rises and parts expand( vw bugs sometimes have the same issue it an air cooled engine by nature the lossen up as they heat up) or som restrictions in fuel float bows full in the Beginning acts as reservoir But somehow the fhell not keeping up try Measuring the flow rate like into a gallon jug on the problematic unit and and a good unit replace float Ball screw with a small hose barb to thead time it and see


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## Micro-Air

*Breaking news: It's fixed!!*

The stator replacement was finally carried out yesterday, and testing was just done within the past hour, and the problem has finally been resolved!! 

In summary, there was a short in the stator that only manifested after the stator heated during full-load operation. This makes sense since the varish on the stator windings does break down after many years of stress and use. I'm going out to celebrate with MANY BEERS! Yahoo!:tango_face_grin:


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## thehandyman1957

WOW, and you deserve them my friend. Amazing how much it took to figure this out. I do hope that others reading this thread will
be able to learn and perhaps even save themselves some work by all your troubles. Cheers!


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## JSLloyd#0424

Newbie to the forum here. I have two EU2000i's, which have worked perfectly for 6 & 4 years, and a brand new EU2200i. The two EU2000i's have Hutch Mountain propane conversions. I found this thread and read every entry from the original post all the way to the solution. Fascinating. I learned a ton. I am somewhat in awe of the level of knowledge and technical sophistication of the members here, not to mention the sheer determination. You are all to be commended. It's going to be a challenge to me to be able to make significant contributions to this group.


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## Captain Overtighten

Micro-Air said:


> *Breaking news: It's fixed!!*
> 
> The stator replacement was finally carried out yesterday, and testing was just done within the past hour, and the problem has finally been resolved!!
> 
> In summary, there was a short in the stator that only manifested after the stator heated during full-load operation. This makes sense since the varish on the stator windings does break down after many years of stress and use. I'm going out to celebrate with MANY BEERS! Yahoo!:tango_face_grin:


Yearrrrrrrs later BUT what an excellent post. Hats off to you microair- an excellent complete process of elimination. I read EVERYTHING- I was convinced it was the coil goofing off as it heated up-but you checked that off the list. We have 5 of these little monsters and they don't live privileged lives. The old girl I'm tinkering with at the moment was half way submerged in a mud hole a few years back. Still ran! I had to wash it out. Still ran! It is still running - rings are a bit tired but she still runs. After a good bounce around in the back of the 1 ton dump box ( like a bingo ball) she won't provide enough juice to run a metabo hammer drill. Tested the 3 phases and read well at 225 +- 18 but they were all even through out rpm changes. 127 V output. The engine doesn't seem to kick in to provide more demand. Tried a 5” angle grinder simultaneously trying to get it to respond. Thoughts?


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