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onan twin opposed m23 engine popping then runs fine

C

case310350

New User
Have an old onan engine/welder twin cylinder. The problem is one cylinder about 1/2 the time will start popping, you can see some flame in the exhaust when this happens and with your hand over the exhaust you can feel the popping. then will start running fine for a while and then start again. its not the gas, or a manifold leak

the other cylinder runs fine all the time.

So looking for some suggestions. Could it be a valve that is sticking?
 
Many things can cause problem you have,some of the more common causes are plug going bad,coil going bad,insulation on plug lead dried out/has hairline cracks & spark shorting to block,sticking/leaking valve,carbon buildup on valve/valve seat,worn valve guides,loose valve seat,head gasket that's starting to leak,worn cyl/rings,sticking,damaged or broken ring,gasket leaking where intake mainfold bolts to block,loose carb/carb mounting gasket leaking,hairline crack in manifold or a problem in fuel system itself.What you have to do is try and isolate problem to ign system,fuel system or an internal mech problem on/in eng,I know this isn't fun,but there are too many things that can cause problem & you may have more than one cause of problem.
 
If it were mine I would try adding some Marvel Mystery oil to the gas and see what happens.
Sticky valve sounds plausible to me.
 
Most common problem with the Onan twins. Was a sticking valve. For some odd reason. It always was the left side looking from the front.

Onan tech since 1980
 
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