Ask The Editors: Gas in the Crankcase
The most common reason for gas to accumulate in the crankcase is, as it seems you suspected, badly worn rings. Gasoline naturally finds its way into the combustion chamber thanks to the gravity fed nature of the carburetor. Ordinarily it can sit on the top of the piston in the cylinder indefinitely as the rings should form a water-tight seal with the cylinder wall.
However, when the rings wear down to the point where there is a gap, the fuel flows freely down into the casing. With a modern fuel injected engine, this process would stop once the vehicle was off and the injectors were no longer spraying fresh fuel. However, the design of ATVs of your vintage placed the tank above the carb so that gravity was in charge of getting fuel into the engine. Unless you turn off the petcock, it’s a pretty straight shot whether the machine is running or not.
We’re sure that fresh top end/ head gasket will get you in good running shape and cure the smoking as well. If by some rare chance you’re still getting fuel in the crankcase after performing the refresh, the last place to look is back to the carb itself. You said you went through it but a stuck float/ seat can also cause a limitless flow of fuel to spill down the intake and through the valves. This, in conjunction with worn rings as discussed above, and you have the potential for the entire tank of gas to dump into the bottom end over time.
