Its your float bowl. In the carb the bowl has a float that works a needle valve shut when bowl is full. There could be debrees thrash in the fuel line, or the float needs adjusting.The filters in the tanks on these are notorious for clogging or falling apart . A in line fuel filter is recommended. This link might shed some light on the subject! http://motorbicycling.com/f30/motorized-bicycle-carburetor-install-rebuild-302.html