# Honda EM3500S low output voltage at idle



## taitkj (Oct 29, 2019)

I have a 30+ year old Honda EM3500S that I just put a new carb in. The old one leaked and caused the generator to speed up and down with auto-throttle turned on. I just put a new OEM carb in and she purrs now.

New problem though. If I leave auto-throttle turned on, the output on the 120v plugs is around 100v (with or without a load). If I turn auto-throttle off and let it ramp up, the output voltage jumps to 120v.

If I leave auto-throttle off and plug stuff equipment in, it does not throttle up.

The generator sat for many many years without running. That being said, it started on the first pull.

Anyone have any ideas on where to start? I hate to get a new AVR just to try as the OEM ones are close to $200. Thanks!


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## tabora (Sep 6, 2018)

I'm kind of confused by a couple of your statements. 

The purpose of the Auto-throttle is to allow the generator's engine to drop to idle speed when no load is applied to conserve fuel. There will not be useful voltage available (low volts and frequency). As soon as a load greater than 1Amp is applied, the engine should go to 3600RPM where it will produce 120/240V @ 60Hz. When load is removed, the engine should drop to idle again. 

It sounds like the generator is producing the correct voltage at 3600RPM with the Auto-throttle turned off? I would guess that the issue would be in the Auto-throttle unit 36210-ZB4-014 or the solenoid 36160-ZB4-013 and not in the AVR. See diagram on page 39 of the Owners Manual: http://cdn.powerequipment.honda.com/pe/pdf/manuals/31zb4030.pdf

Here's an auto-throttle troubleshooting procedure I found:

Inside the control box on the generator the power leads get connected so that we have an L1, L2, and N feed wire with L1 and L2 being the 2 "hot" wires. Both of the hot wires pass thru a small current transformer (one wire in each direction) and then go to the various outlets in the output panel. The current transformer makes a signal whenever current is drawn thru either wire.

The current transformer sends its signal to an idle control circuit on a printed circuit board inside the control box. The other wires from this board go to the idle control switch, the power regulator/exciter board, and the idle control solenoid. The idle control board uses the DC voltage it gets from the regulator/exciter to energize the idle control solenoid if the idle control switch isn't in the "off" position and no signal has come from the current transformer for a sufficient time. The idle control solenoid acts to pull the throttle assembly until the throttle bell crank hits the idle adjustment screw.

Troubleshoot it like this:

1 - Does the engine start at governed speed and then idle down or does it start at idle? If it starts at idle, or seems to idle down faster than usual, something might be amiss in the works.

2 - When you turn the idle control switch to "off" does the engine rev up to governed speed immediately? If not there is almost certainly something ugly going on.

3 - With the idle control solenoid unplugged from the idle control board does the engine rev up to governed speed? If it won't you need to check to see if the plunger is stuck on the idle control solenoid. Some solenoids also have an adjustment that can get loose, check the voltage on the wires coming out of the idle control board if you're in doubt about its being energized or not.

4 - If the generator revs up when you turn the idle control off, but won't do it automatically when current is drawn with it turned on you need to check the current transformer with an ohm meter. Even though this is an AC signal you should mark the leads when you take them off so that they go back from whence they came - it's a noise thing. ;-) Little square current transformers are usually somewhere in the 1 - 2 KOhm range, failures are typically that the coil opens up.


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## taitkj (Oct 29, 2019)

Good morning Tabora. The generator does idle down when nothing is plugged in. Now that I am reading your reply, it makes sense that it does not put out 120v at that time. The auto-throttle is doing what it should.

If I turn-auto-throttle off, the generator speeds up to 3600RPM and creates 120v.

If I leave auto-throttle turned on and plug something greater than 1A in, it does not speed up to 3600RPM. Based on that and your information, the issue likely lies in the auto-throttle.

Thank you for the extensive information. I will be using that to help troubleshoot further. #4 is what I am experiencing but could have issue #3 as the control arm coming out of the auto-throttle to the carb has to be moved in order to remove the carb. Time to get the meter out and start testing the current transformer.

Thanks Tabora


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