Always give year, make, engine size and model # when asking questions. We need all of that info to give an informed answer.
2 & 4 stroke engines can have similar problems requiring different repair procedures.
Most common problem would be the carburetor float needle leaking, allowing the float bowl to over fill and the gas spilling into the cylinder.
If this problem is happening on a 4 stroke engine, it's imperative to get it fixed ASAP. Do not run the engine!
The engine can become "hydrolocked" and bend the connecting rods.
http://www.reference.com/search?q=Hydrolock
A 2 stroke engine - if the plug was fouled and not igniting the fuel, the bottom end would fill with gas and flood the engine.
