Onan AC Generator Wouldn't Start

by Don Archer
(Peachtree City GA)

My Onan AC generator would not start, and I knew that it was a gasoline problem. I tried starting fluid which caused it to run for a few seconds and tried carburetor cleaner which didn't do any good. I made an appointment to have the carburetor replaced on this Genset for a charge of $500. Fortunately the snow storm hit Atlanta the day I was supposed to take it in.


I decided to try one more time and removed the gas line going to the carburetor on this AC generator, held it upside down, and drained as much gas out as possible. Then I sprayed straight carburetor cleaner into the line and reconnected it to the carburetor.

After fighting this problem for a couple of months, the AC generator started right up. I let it run with a couple of bottles of SEA FOAM added to the gas tank. This genset has been starting right up and running great ever since. Hope this helps somebody else.

Editor's Note:

Don is to be commended for his persistence and diagnostic skills. This genset is probably one of the most temperamental systems on a Class C Motorhome. I'd like to add a few thoughts here because I feel that with a little additional information, an issue like the one in Don's story can be easily avoided. Having said that, here goes... all gensets need to be babied for two big reasons:

1. Exercise

Onan recommends that their generators need to be run at least 2 hours each month at 50% capacity. Unfortunately, not running your AC generator can cause a buildup of gum or varnish type substances that can, over time, block the small orifices in any carburetor. This will potentially prevent your genset from starting. It can also make the system run rough with a surge effect. Don was correct in first assuming that his carburetor was the culprit with his malfunctioning generator.

2. Ethanol

The E-10 fuel we use today is hygroscopic. This Ethanol fuel tends to suck moisture out of the air and deposit it at the bottom of our fuel tanks. Of course, this is precisely where our fuel pick-up is located.

Water in the fuel line is a major reason many lawn mower motors do not start in the Spring. Folks, when you boil it all down, your AC generator is just a big lawn mower engine. Water in the line could have easily have been Don's issue.


There are a couple of things you can do that will inhibit this scenario, but I'm only going to recommend one. Keep your tank full when you are storing your Class-C-Motorhome. It is important to understand that Ethanol cannot absorb moisture out of the air if it isn't in contact with air. A full tank will prevent this type of contact.

Again, I want to thank Don for bringing this important subject to our attention...

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Aug 01, 2016
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Nov 10, 2015
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It can NEW
by: Clark_T

It can also make the system run rough with a surge effect.

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Nov 04, 2015
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Onan AC Generator Wouldn't Start NEW
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Oct 30, 2015
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Oct 22, 2015
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Great post NEW
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Oct 21, 2015
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Oct 21, 2015
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Good NEW
by: Steven

My Onan AC generator would not start, and I knew that it was a gasoline problem. It is not big problem.
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Oct 21, 2015
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Oct 08, 2015
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Jun 15, 2015
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Class C Batteries NEW
by: Anonymous

Along with starting your genset for 2 hours every month and loading it to 50%, you really need to check your batteries. Make sure that your batteries look good, not bulged out and have enough electrolyte in them to operate correctly. If not, go buy some distilled water to fill the battery to the correct level.
Ensure your battery cables are not corroded. Corroded battery cables will not allow enough power to pass thru to the started solenoid to make your started engage.
If your batteries are very low, your batteries will only charge at 3 to 5 amps if you are charging on a 50 amp system. Any lesser system and they will not charge as fast.

Jun 13, 2015
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Onan generators class C generators ... Fix gumming up problem NEW
by: Anonymous

Put a shutoff valve to the gas line... Any RV repair facility can install this. When not using the generator, run the gas out of the carburetor like a lawn owner ... Till out of gas. Easy way to fix and not expensive!

May 19, 2015
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save fuel NEW
by: Earl Lofton

I Fixed My Problem With A Fuel Shut Of Valve From A Lawn Mower Place. Instead Burning Fuel My Generator 2hr Every Month.

Aug 10, 2014
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power converter NEW
by: Anonymous

my power converter is located under the dining table seat.

Aug 10, 2014
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by: John L.

I recently bought a 1985 Fleetwood Rallye on a Ford E350 chassis. I blew a fuse or tripped a circuit breaker, and the manual states it is located on the power converter...but where is that? I have looked everywhere I can think of, inside and outside the unit.. someone, please help?

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