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Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14994
Experience:  Certified on Onan and Generac generators
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I have a natural gas onan generator, Cummings engine model

Customer Question

I have a natural gas onan generator, Cummings engine model 12GRCA-4229A. Recently is has sounded like it's running "rough". When I listen from the exhaust side it sounds like it's misfiring, but when I listen to the engine directly I am unable to appreciate that. It almost sounds like it constantly "clearing it's throat". For awhile this would straighten out after about 5 minutes and then hum like a kitten, now it's not stopping. Spark plugs didn't help. The engine is not shutting down and giving me a flash sequence signal. Thanks.
Submitted: 2 years ago.
Category: Small Engine
Expert:  Hank F. replied 2 years ago.
My name is ***** ***** I am going to assist you with this.
The place to start with an issue like this is with a good, old-fashioned tune up. New plugs, properly gapped, air filter and valve adjustment.
When you changed the plugs, are you sure you got the correct ones?
Did you properly gap them to .030" - .040"?
Install a new air filter.
Check valve lash, and adjust as necessary.
Intake valves should be set to .006".
Exhaust valves should be set to .008"