Onan/Cummins generator

6869704x4

Member
I have an Onan Elite140 driving a Pro 5000E generator.
This thing is backfiring pretty bad. It shoots a flame about a foot out of the carb with a corresponding shotgun blast noise. You should see it at night! The troubleshooting chart in the Onan service manual lists possible causes as,
1.Magneto gap wrong-I checked and its OK
2.Fuel mixture too rich- There aint a mixture screw on the carb.
This puzzles me because I was taught a lean condition usually causes backfire.
3.Engine flooded- Not as far as I can tell.
4.Fuel quality poor-Nope, fresh gas.
5.Carburetor Dirty-Took it apart and cleaned it.
6.Air Cleaner Dirty-New one.
Any other ideas out there?
Time to check valve timing/condition?
 
poss, intate valve sticking sometimes, maybe spray some treatment into carb while engine is runnung then shut off quickly to let the stuff work into valve guide???
 

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