I have had this same problem many times in the past with mine. There are a couple of things that have caused it over the years though. The clutch cuttoff was one cause. The switch in the clutch lever to prevent starting until the clutch was depressed went bad and I ended up cutting out the switch all together instead of replacing it. Another problem is that the wires from the coils switch colors at one of the connectors. This is a strange one but my wiring diagram proved it when I got to sit down and read it. The biggest cause for me and that problem though is the fuse box. The connectors for the fuses started to corode a little and while it showed I had power and should run it was not enough to turn it over or fire it. Try these out and tell me if they help.