John Deere STX 38 GAS IN THE OIL

[RPM]

I have a 1996 STX 38 black deck lawn tractor with a Kohler Command 13 engine. I got the mower for free from a guy who thought the engine was bad (actually, he quietly told me that he didn't think it was too bad, but it made a funny noise while his wife was mowing. They had a lot to mow, so he wanted to buy a bigger and more comfortable mower so his wife would continue mowing). Turns out the butterfly plate in the carb came off. Reinstalled that, plus a new belt and sharp blades, and it has worked and run great for about 4 years now.
However, when I changed the oil last week, I noticed the engine was over full and the oil was thin and smelled like gas. Is there anything besides the carb that would cause this? When I remove the air filter I can see a small pool of gas straight down below the filter. Plus, the tractor will backfire occasionally when I shut it down.
I did have a little trouble starting the mower this year, so I cranked it over quite a bit before buying a new plug. Started right up after that. Don't know if all the cranking might have dumped gas into the oil, but I think it was already in there.
Thanks for any help or ideas.

 

[ILENGINE]

Sounds like the classic needle valve is leaking causing the carb to overfill with gas, then running into the cylinder, or through the breather into the crankcase. The carb needs cleaned and the needle valve replaced.

 

[Rivets]

I would also start using non-ethanol fuel if it is available in your area.

 

[HarryHarley]

You could also put a fuel shut off between the fuel tank and carb. Then turn off fuel and let motor shut down for lack of fuel.
Temporary fix until you get to other issue. Plus you should do that anyway. Good luck. Let us know your results.

 

[RPM]

Thanks for the ideas. So it sounds like it is something not too major. I wanted to check before diving in- is it possible it may be deeper, like stuck rings? I guess we start with the easiest first. If that fixes it we are good to go.
I have started using non-ethanol fuel. My local John Deere dealer suggested it and told me where to find some. All my small gas engines are changing to non-ethanol.
I will let you know.