I have a 1-cylinder, overhead cam, 15HP Kohler in my lawnmower. It has just started putting gas into the crankcase. I had a mechanic do a compression test, and I’ve got good compression. I had my carburetor rebuilt, changed gas/air filters, changed oil, but when I run it for about 30-45 min., and stop and check it, there’s excessive gas in the oil (I mean a lot of gas). Any suggestions on what I need to check as to what is causing this problem?
Did you have all the work done on it in response to the gas in the crankcase problem, or did the problem develop after that work was done? And it’s only happening when the engine is running?
The most common gas-in-oil problem with small engines is that the carb float gets stuck and overflows into the cylinder, but if it’s only happening when the engine is running that’s probably not it. Plus the carb rebuild would have fixed it (assuming a botched rebuild didn’t cause it in the first place.)
Does this mower have a vacuum fuel pump? That’d be my next best guess, although there could still maybe be some issue with the carb adjustment with fuel getting into the crankcase via the breather system.