Hi. Suddenly the petrol in my Stihl KM94 RC (2-stroke) has started dripping out of the carburettor into the air filter. The machine still works (although I have had to remove the sodden air filter) but it is getting through petrol mix at a right old rate (and is probably dangerous too). The petrol leaks out even when the machine is turned off, lain on it's back and even when the tank is virtually empty. It's almost like some siphon action is at work. I've looked around a bit and all I can find