check the fuel cut off selenoid attached to the carb or fuel pump, it could be faulty, and not cutting off the fuel when you turn off the ignition. You've probably sorted it by now lol. Just screw it off, leave it conected to electric wire. Then turn on your engine, but not to start. If the plunger inside retracts then it is o.k if it does nothing replace it.
Ray., June 2006