Fuel in Oil

I am working on a Ariens RM9030E with a Briggs and Stratton 12.5 hp IC/Quiet engine and I am stumped with the following problem. After sitting overnight the fuel tank will be completey empty and all the fuel will be mixed in with the oil. This happened once when the rear of the lawn mower was elevated so I drained the oil and replaced and sure enough it happened again with the lawnmower flat. A little history on thie rider, it sat outside for 2+ years without being started or touched. I had to drain and replace fuel, clean out carb, and replace spark plug just to get it to start. However it runs fine now after the oil/fuel is replaced. But then it drains back into the oil system overnight. Anyone have an ideas as to what could cause this? Did I mess up something in the carb?
Thanks

 

Needle stuck in carburator or bad float in carb.

 

Agree with the stuck needle or bad float in carb. If you have a engine that has a fuel pump on it it could also be a bad fuel pump.

 

I would add to what ducky and J&R said, the float needle may be worn on the tip or have some debris on it

 

Same problem with '01 White LT 1650 ... my gas drier may have caused the distorted fuel pump diaphram in my 4 screw fuel pump carburetor ... added a fuel line shut off twixt tank and carb ... still have some problem with ocassional flooding ... another float and valve?
am considering buying a new carb ... mine is wierd, 4 screw fuel pump #692812 ... most common is 3 screw #693480 ... wonder if it's an emissions thing?

I'll keep checking in and reading ... L8R, miklb o)}

 

I agree that it sound like a needle gone bad, take the carb appart and see if the needle has a rubber tip or solid metal. If its metal then you need to replace the rubber seat in the carb, can be trickey if you have never done before. The best to see if the needle is sealing off is to take the carb off and the bowl turn it upside down and blow into the carb inlet and see if it fells likes its sealing. When you go to get the parts invest in a inline shut-off valve to put in fuel line, usually less than ten bucks, so you can shut-off the fuel when you are not running it, call it piece of mind. Good luck