Is it one of the Torch Plugs, if so get rid of the plug and get an NGK, not sure of the number but someone will be able to give you the correct one here. Make sure your needles are set to run smooth also check for any seal leaks. Some CRRC engines seem to a little difficult at first and improve quite a bit once you run some fuel through them at least a gallon or so, do not run them over ritch like you would a glow engine. (you will never seat the rings if you do)