A couple of other things on this project: fuel flow must be shut off automatically if the engine dies. There are two ways to do this. 1- by engine vacuum turning on a shut off valve when engine is cranked(safest). 2- electrically with an electric shut off valve. This valve needs to be controlled by vacuum, oil pressure, or electrically,i.e engine not running, valve closes. The other thing is as I said before, the fuel and air must be mixed before entering the carburetor. Yes, you can use the existing carb to control enrine rpm, but the gasoline needs to be shut off. There are mixer adapters made which normally mount between carb intake and air filter. BTW, what kind of machine,i.e. make and engine are you thinking of doing this on? I'm just giving general info now, but could give more specific stuff w/ that info. You still need a butterfly in the system to control throttle. Ideal air/fuel ratio is 14:1.