Be sure that your carb heater valve is turned off, that is the little red lever on the valve that controls the flow of antifreeze to the carbs to keep them from freezing in below zero weather or when the humidity is high (frosty), if the antifreeze is allowed to flow to the carbs in warm conditions I have found that when you shut the motor off the carbs will overheat and vaporize the fuel or cause it to expand and flow into the motor causing the motor to flood.