Gary,
It can be anyone of the items Jason mentioned. Usually it is the CDI starting to fail. Before you condemn it though, verify it isn't a coil by switching them. Swap the primary and secondary wires together. Problem should follow the coil if it is bad. Another issue on the early models has been the gap for the pickup coil. It should be .8mm instead of the 1mm. This has corrected problems in the past but I'm a skeptic. It usually is an indication that the CDI isn't processing the signal the way it could in the past. So something is failing.
Fast Eddie sells the Procom replacement unit which is less than half the price of new.