Onan Marquis 7000 Dies Under Load

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G

g4h2o0st

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Sep 29, 2016
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Hello,

I have a 1991 Pace Arrow with a Onan Marquis 7000 genset.

The Model Number is 7NHMFA26106B and I have several issues, most importantly the generator dies whenever the A/C kicks on.

I have:
-Changed the plugs... the inner plug was badly fouled.
-Changed the oil.
-Changed the oil filter.
-Changed the Onan fuel filter and added a clear, inline filter so I can verify fuel flow.
-Checked the cylinder compression on both cylinders. Both are kicking out 90 psi.

So, I am beginning to think this may be a carburetor issue. I am looking for a carburetor rebuild kit, but am having problems.
I am also considering the control board and governor.

Any ideas would be appreciated.

 
Carburetion is the usual problem in a gas genset, especially a vintage model like that. The carb on a small engine is hellishly sensitive to invisible plaque & dirt in the tiny passages. Try a Carb cleaner additive, e.g. Seafoam and maybe you will get lucky. If not, rebuild or replace the carb.

You can mix carb cleaner in a gallon fuel container and divert the genset fuel intake to that container.
 
You usually can find a carb gasket kit on eBay very reasonable. I have the same generator and when mine has had your symptoms, it was ALWAYS the fuel pump. 3 times in 20 years. In my experience, if they run ok under a light load, the carb is ok.
 
Does the engine hunt for RPM when under load? If so it is lean. I assume you have tried to adjust the the altitude compensator? If you are uncomfortable disassembling and cleaning the carb, a small engine shop may be able to help.

 
Hey Guys,

Here's an update... I ran a couple of gallons of fuel and carb cleaner though the system, hasn't helped. I am going to break down the carb this weekend and I need to identify the precise carburetor I have.
 
Dont do the carb,  do the fuel pump first.  This was the same problem I had, and the pump fixed it.
 
Hey Everyone,

Here's an update...

-Installed new fuel pump.
-Installed new clear inline fuel filter.

Same problem, runs like a kitten until put under load and then it dies immediately.

Next Ideas:
-Carburetor Rebuild
-Replacing brushes (Does anyone have exploded views or diagrams showing the location? Instructions?)
-Replacing Control Board.

Thanks ahead of time for any advice.
 
Carb is probably a good bet, but I'd check the gas lines first. A pinhole leak or collapeed line can result in the symptoms you describe.

Ernie
 
Does the engine cut out like the ignition is being switched off, or does it stumble a bit and then die?

The first points towards possibly being ignition or control board related, the second carburetor or fuel delivery, since it takes a second or two for the fuel level to drop in the carburetor bowl before the engine fuel starves.

Don't forget the engine is at full throttle when you start it, until it comes up to speed and overcomes the intertia of the flywheel and generator armature.  The difference is the choke is fully on at startup, which can mask a carburetor problem.

Try holding the choke partially on while adding the load and see if the engine responds differently.  If it does, it indicates a carburetor problem.  If it still immediately cuts out, it may be the control board cutting out the ignition.
 
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