I had to trouble shoot my ignition last year, and after trying a bunch of stuff (regapping the coil, regapping the plug, getting a new plug, etc), it came down to having only a couple of wires attached to the plug connector on the plug wire.
Sure, it's not really a common thing that happens I'd say, but it's cheaper to inspect and be sure of than going out to get a new coil at least.... especially if the motors getting up there in age.
All I did was pry the crimped ends open, cut down the wire's covering and reattach it.... then while testing it, I got zapped and knew had made a good connection