The float needle in your carb is not closing properly. This is resulting in fuel flowing nonstop from the tank, through the carb, into the cylinder causing hydro locking. Remedy, you will need to remove the carb and replace the float needle and possibly the seat, depending on which brand of carb you have. Oil will also need to be changed, as it is probably contaminated by fuel flowing past the rings. Some fools will say to just install a shut off valve in the fuel line and make sure you turn off the fuel after each use. If you forget, you will be back to the original problem. I always recommend fixing the problem right the first time, but make sure you read my signature.