* Worn piston rings. The piston rings are responsible for sealing the combustion chamber and preventing fuel from leaking into the crankcase. If the rings are worn, they can no longer do this job effectively and fuel can leak into the crankcase.
* Damaged cylinder. A damaged cylinder can also cause fuel to leak into the crankcase. If the cylinder is scratched or gouged, it can provide a path for fuel to leak into the crankcase.
* Float needle valve stuck open. The float needle valve is responsible for controlling the flow of fuel into the carburetor. If the float needle valve is stuck open, it can allow too much fuel to flow into the carburetor and some of that fuel can leak into the crankcase.
If you think your motorcycle may have fuel in the crankcase, it's important to take it to a qualified mechanic to have it diagnosed and repaired. Riding a motorcycle with fuel in the crankcase can damage the engine and cause it to seize.
