# Honda EM3500 SX auto choke not closing



## darcyh (Jul 4, 2011)

Hi Folks:
I have the above generator and this problem is driving me nuts!

I can start it using manual choke, once engine starts running the vacuum choke servo or diaphragm will pull the choke open. When I shut engine off, the choke remains open and the vacuum diaphragm continues to pull on the choke leaving it open.

If I disconnect the vacuum line to the diaphragm, it releases and the choke returns to closed position. Unless I disconnect the line, the vacuum stays applied to the diaphragm even when engine is off. 

There is a check valve and an electric switch solenoid in line with the vacuum hose. Both appear to be working okay. If I apply 12 volts to solenoid it 'clicks' and closes, not allowing any flow. Disconnecting power to solenoid it 'clicks' and allows air to pass through it. The check valve also seems to be okay. I can blow through it one way but not the other.

For the choke to come on, there seems to be a need for the applied vacuum to the choke diaphragm to be released or dissipated before the diaphragm will move and allow the choke to return to closed position. This is not happening, in other words the vacuum applied to diaphragm is held constant or never removed preventing the choke from returning to closed position. 

Even when this system is functioning properly, I cannot see how the vacuum that's applied to the choke diaphragm can ever be released when the check valve prevents it.

Something has to release the vacuum applied to the choke diaphragm when engine is stopped. What is it? I gotta be missing something here? 

Any suggestions would be appreciated.

Thanks very much.

Dave


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## Robert Coats (Nov 10, 2011)

darcyh said:


> Something has to release the vacuum applied to the choke diaphragm when engine is stopped. What is it? I gotta be missing something here?
> 
> Any suggestions would be appreciated.
> 
> ...


From the shop manual:

_With the engine switch set to START, the choke solenoid is energized by the current from the battery and closes the choke valve. After the engine starts up and the engine switch is in the ON position, current from the charging coil is rectified by the bridge diodes and keeps the solenoid actuated through the thermoswitch.

When the engine temperature rises above the specified temperature (see table below) the thermoswitch in the cylinder head opens the circuit and the choke solenoid is deenergized. Vacuum then opens the choke valve. The Manual Choke Lever overrides the Auto Choke System._


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## darcyh (Jul 4, 2011)

Hi Robert:

Thanks for the reply. I understand what you are saying and can visualize how this should work. And it does this initially if vacuum is not present at the diaphragm. BUT with my EM3500S, the vacuum line from choke diaphragm is connected to a check valve (Honda calls it a check valve / dash pot, part number 36135-ZV1-003) then to the auto choke solenoid valve. So even if the auto choke solenoid valve opens, the vacuum will still be held at the check valve. 

I think the problem with my unit is the vacuum force that holds the choke valve open is not being released when the engine is stopped.

With engine off, the only way I can get the the choke valve in carburetor to close is to use the manual lever, or disconnect the vacuum line at the diaphragm.

Simple diagram (forgive its crudeness please) ---> is direction of vacuum
<=== atmospheric pressure or release air

Choke diaphragm ---> check valve or dash pot ---> auto choke solenoid ---> source of vacuum at carb intake

So when auto choke solenoid opens and allows flow, the vacuum will still be maintained by the check valve / dash pot and therefore the choke valve will remain open. How is the vacuum released? To me it looks like a one way system. Since it used to work, the only thing I can imagine is that the "check valve / dash pot" Honda part number 36135-ZV1-003 must open up to release the vacuum as opposed to a true one way check valve. That's the only way I can envision the vacuum being released.

Do you think I should replace this check valve / dash pot?

Thanks again, so much for your assistance.

Regards,

Dave


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## darcyh (Jul 4, 2011)

*Solved!*

Thought I would follow up with the solution for anyone else that may experience the problem.
Replacing the 'dash pot / check valve' solved the problem. It allows the vacuum to dissipate once the engine has stopped. This action engages the choke.
As Robert stated above, once the engine is started and warms up (about 2 minutes) the thermal switch activates the solenoid and engine vacuum is applied to diaphragm which opens the choke valve. I don't think the automatic choke ever worked properly on this genny until now.

Regards

Dave


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## Gord (Apr 17, 2020)

darcyh said:


> *Solved!*
> 
> Thought I would follow up with the solution for anyone else that may experience the problem.
> Replacing the 'dash pot / check valve' solved the problem. It allows the vacuum to dissipate once the engine has stopped. This action engages the choke.
> ...


I had the same problem. I tested the check valve with a vac pump fro a brake bleed kit. It held a vacuum solidly. I the blew the valve with compressed air in the direction of no resistance. Then test with vac pump and it slowly dropped pressure. The choke works fine now. I feel the valve gets plugged with fuel droplets over time.


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## iowagold (Jan 22, 2020)

I guess this is why I like the new eu7000is..
no choke.
it is tbi fuel injected so choke is done with a pulse of fuel right before the start cranking of the engine.

yea any rubber seating valves is asking for issues over time..


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