The pulse generator is too simple to have a failure. I doubt it is the problem. Replace the spark plug AND the wire. Once the wire carbon tracks, it is garbage. My 650L is on it's third one. I had the same problem as captb with my CDI. It first acted up about two weeks after I bought it in May of 1996.. There would be no problems for a year, then it would quit running for no reason.. I'd pull the plug, there would be no spark.. Then 5 minutes later there would be spark.. Another year or two would go by and the same thing would happen.. I had no idea it was the CDI. It irritated me to no end. Come 2005, it died entirely, and would not spark at all; finally, I could FIND the problem for sure.. I replaced the CDI, and I swear that bike started up before one rotation of the engine. After getting the new CDI, the bike starts up every time quicker and stronger than it did when it was brand new. My bike has over 60,000 abusive miles on it. Which begs the question: Why would those CDI's run so poorly for so long, and not die right off the bat? It was so very frusterating!!!