I have known a couple of people who tried the engine using just muffler pressure. It didn't work. I tried it too and it didn't work for me either. The OEM carburetor is the problem. Now if you replaced the carb with a better one, such as using the Evolution 10cc gas engine carburetor, then it ought to work OK. Or you could make an adapter for using a small bore Walbro carburetor instead. The Walbro carb works well on it.