Sounds like the float in the carburettor float chamber is stuck or maybe punctured, or the float valve is jammed, allowing it to flood. Could be a bit of dirt holding the valve open. Turn off the fuel tap, take the float chamber off, hold the float or the float arm up to close the float valve and see if petrol comes out when you turn on the fuel tap - it shouldn't! Only when you release the arm should the fuel come out. In normal operation when the float reaches the correct level in the chamber it should close the valve until the fuel level in the chamber drops, then the float drops and allows the valve to open again.
Peter T, February 2008
