I suggest you check the TORS. The system consists of a switch inside the body of the throttle and a switch inside the carburetor. When the throttle is at idle, the switch is open.(at the same time, the switch inside the carburetor is closed). When the throttle is increased, the switch inside the hand throttle becomes closed and the switch in the carburetor opens. One switch or the other must be closed to satisfy conditions for a spark. The purpose is to kill the engine in the event of a stuck throttle. In my case, the switch inside the throttle(which is normally open) was faulty. It was an easy fix. I used a wirenut to connect the wires together to fool the system. It was tricky to diagnose, because if the throttle wasn't touched, the engine would start and idle, but would die if you gave it any gas. While checking for good spark, I was lucky to stumble into the fact that there was no spark if the throttle was turned. Good luck.