Small Engines (Lawn Mowers, etc.): Onan twin cylinder 20 hp engine, crankcase oil, exhaust pipes

Question
Engine runs well however  gas is getting into the crankcase oil.  It also appears some gas is exiting one of the two  exhaust pipes.   How do I fix before ruining engine?   Engine has two spark plugs, both are getting sparks however if  I disconnect one plug the engine continues to run however if  I disconnect the other plug the engine stops.  Could one cylinder  be firing and the other not ,even it sparks.
Onan  Twin cylinder 20 hp engine approx 20 years old.

Answer
Hi Lou,

I have heard before of a situation regarding the spark plug disconnecting, where the engine would quit even though both cylinders were firing.  I'm not sure why.  In your case, if only one cylinder were firing, that would cause the other, to push fuel out of the exhaust port and maybe into the crankcase.  You say that both plugs fire though.  If you can't tell by sound if both cylinders are firing, then check to see if both plugs are dry.  Also try swapping plugs, then inspect them.  Check compression in both cylinders.

Finally, gas in the oil sometimes is caused by a carb float related leaking problem. It might be dirt, the floats' needle and seat valve or a fuel logged float.

Let me know how you make out.
Michael