Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

The carburetors on these engines are pretty crude.  It’s easy to twist right past a very narrow sweet spot, especially when everything isn’t perfect.  Fuel? I’ve been there and back with zippo. It’s simply not very energetic, so it doesn’t suffer anything less than great very well.   Gasoline as sold for motor fuel is more energetic, but suffers storage issues. Old gas, bad gas, etc are real things.

So if you sent me the engine, I’d first completely flush and blow dry the carb and fuel line. I’d refill the tank with known to be good gasoline with about 50:1 marvel or two stroke oil, Then insure the engine will suck fuel when cranked. Any bubbles present in the gas line should move when you crank the engine briskly.  Set the needle at 1/4 turn open, and in steps no more than one clock position, open the needle and retry.
If you thumb choke and hand crank until the line is full of fuel and your thumb gets wet, then turn on the battery and drill spin it briefly, the engine should at least pop if it’s anywhere close.
What these engines don’t like is leaks. The carb vacuum is weak, so fuel lines can’t leak or you lose suction. Persistent air bubbles can be maddening. Get em gone. I’ve literally used a needle oiler to refuel, and sucked air bubbles out of the line with the needle, by way of the filler cap.
Insure flywheel set screws are tight. A slipping flywheel will put one of these engines out of action, and until you grab and twist, you might not know one was loose. Just stuff my m91 taught me.