Rough running Genny

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

mylo

Well-known member
Joined
Oct 1, 2012
Posts
220
Location
Phoenix, AZ
I know it's next to impossible to diagnose many problems in a forum, but I was looking for some input on my generator. I'm pretty good at diagnosing and fixing normal, small gas engines - like for lawnmowers and weed wackers... But I haven't worked on many generators.

It starts right up - but oscillates throttle. Not deeply, but enough to be annoying. I'm thinking that there is probably some varnish built up in the carb, having sat for so long. It's probably slightly starved for fuel. The governor thingy is probably revving it to keep it running. What would you guys suggest I try? Cleaning out the jets? I already replaced the fuel filter and spark plug.

Thanks.


Mylo

 

SeilerBird

Well-known member
Joined
Feb 25, 2012
Posts
15,962
Location
St Cloud Florida USA
If it is an Onan then I wish you good luck. I fought mine for a year and finally gave up and had another one installed. It ended up surging too. I sold the RV. I would suggest rebuilding the carb. It is not that hard to do. All the info can be found online if you look up the model number. You might want to let us know exactly which gen you are talking about.
 

RoyM

Well-known member
Joined
Apr 11, 2009
Posts
1,972
Hold the throttle steady with your finger, if it smooths out and runs fine the governor is too sensitive. If it stumbles you have a carb issue.  What fuel does it run on?
 

mylo

Well-known member
Joined
Oct 1, 2012
Posts
220
Location
Phoenix, AZ
RoyM said:
Hold the throttle steady with your finger, if it smooths out and runs fine the governor is too sensitive. If it stumbles you have a carb issue.  What fuel does it run on?

It's gas. Made by Onan. Model # 4BGEFA26100G


Mylo
 

carson

Well-known member
Joined
Sep 1, 2006
Posts
4,919
Location
Florida, USA
I had a 4BGE....  Here's another idea.  Sounds like a fuel/air mixture problem.

  First thing that comes to mind is a dirty air filter. (air restriction), or a carburetor fuel needle adjustment.

  The governor adjustment is difficult and should only be adjusted if engine speed, under smooth operation, is too high or to too low. The last to thing to attempt to solve the problem.

  Try the altitude range adjustment on the car.

 

mylo

Well-known member
Joined
Oct 1, 2012
Posts
220
Location
Phoenix, AZ
carson said:
I had a 4BGE....  Here's another idea.  Sounds like a fuel/air mixture problem.

  First thing that comes to mind is a dirty air filter. (air restriction), or a carburetor fuel needle adjustment.

  The governor adjustment is difficult and should only be adjusted if engine speed, under smooth operation, is too high or to too low. The last to thing to attempt to solve the problem.

  Try the altitude range adjustment on the car.

The troubleshooting grid did say that a "hunting governor" (surging back and forth) was also caused by a dirty carb. I'm thinking that is the most likely explanation - considering how long the unit sat without running. I'm gonna get a rebuild kit and clean it out.

I should have mentioned - I did change the air filter, too. Also, I did notice that the little flapper for "summer/winter" had broken off it's pivot. Consequently, it is permanently in "winter" mode - which draws some warmer air from near the manifold. The ambient when I was experiencing the problem was probably 85 or so. Not sure how important that little piece of plastic is. I suppose I'll get a replacement when all else fails to solve the problem.


Mylo
 

Lou Schneider

Site Team
Joined
Mar 14, 2005
Posts
10,956
At 85 degrees, adding more hot air via the winter flapper is probably pushing the carburetor temperature close to vapor lock.  Modern fuels are very different than what we had a few years ago.
 

Foto-n-T

Well-known member
Joined
Jan 1, 2012
Posts
1,121
Location
Cody, Wyoming - Sometimes
It's my understanding that rebuild kits are not available for Onan gensets, replacement is the only option that Onan has but you can probably save it.

Get your hands on some SeaFoam additive and double the theraputic dosage.  Run the genset under load for several hours and keep your fingers crossed.  I had to do this a couple of years ago and it drove home the necessity of exercising your genset once per month.
 

Sloop

Well-known member
Joined
Oct 19, 2011
Posts
267
Location
San Marcos, CA
I think Joe has the right idea. Try and clean it with a strong solution of Seafoam. If that does not work you might try this. Last year I had the same problem with my Onan generator.  I removed the carburetor and intake manifold and cleaned them both. Just because you cannot order a rebuild kit does not mean the carb cannot be cleaned.  What was interesting was I found a lot of resin buildup inside the intake manifold but not so much in the carb. The majority of the resin was at the turn in the intake manifold where it provided intake to the cylinder farthest from the carb.  I suspect the resin buildup was affecting the vapors being presented to that cylinder causing them to liquefy before reaching the cylinder.  I cleaned the intake with an aerosol brake cleaner and the carb with a carb bath and compressed air.  The generator runs fine now.  Onan recommends you remove the intake manifold when removing the carb otherwise I would never have found the resin in the manifold.
 

mylo

Well-known member
Joined
Oct 1, 2012
Posts
220
Location
Phoenix, AZ
Foto-n-T said:
It's my understanding that rebuild kits are not available for Onan gensets, replacement is the only option that Onan has but you can probably save it.

I found several people selling rebuild kits, but they are certainly a little pricey at $70. Obviously better than spending $170 on a new carb. I'll try the seafoam stuff, first. Then probably a manual cleaning.

Thanks, guys.


Mylo
 
Top Bottom