chances are good you have bad float in the carberator and that is letting the gas run through from the gas tank to the engine. When the float is down or loaded with gas it will not hold the check valve closed and as a result you get flooding of the engine or too much gas and it runs right through to the muffler. The spark plug is wet with gas so it won't fire. The float may just be stuck down and needs to be freed up.
Gerry, September 2007
