the CZ series are OLD engines. If the compression isn't high enough you might be getting flame-outs when you try and give it gas. Look up the paper work for the CZ engine on OS's website and get the factory setting from there. If you know how to tune an engine you are in good shape. Check for all the usuall problems with engines (pressure line leaks, tank leaks, fuel line leaks, bad seals in the engine/carb, glow plug......).