Try this. I ran into the same problem and it took forever to find. Pull the spark plug wire off and put a plug in it. Place it where you can see it while sitting on it. Kick it to see if you have spark. "IF YOU DON'T" Then try pushing the thumb throttle a little bit and kick it over. IF you have spark then it is the little black box inside the thumb throttle. You can either replace it or cut and splice the two wires going into the thumb throttle together. Hope this helps cuz it was a royal bitch to find on my old shee.