[Jeff Higgins]

I'll actually go out on a limb and say that plug looks fine to me. It's not the problem.

Air-cooled, carbureted bikes need to run a little fat. Most will do so when operated at less than WOT, balls-to-the-wall riding, just so they don't lean out too much when you are riding in that mode. I think a lot of guys get used to seeing pristine, light ash colored plugs common to modern fuel injected motors that do a much better job of controling A/F accross the full range of throttle positions and loads, and assume all plugs need to look like that.

Well, they don't. Carb's just can't provide the accross the range mixture control that EFI can provide. There are rich spots and leans spots. The lean spots drive the tuning. In other words, the leanest condition cannot be so lean as to damage the motor. Everywhere else in the range just gets richer from there.

I doubt the carb's are the problem, jetting or otherwise. They don't operate in an "on/off" mode, where the cylinder either fires or doesn't. Electrical components do that. If it still has the stock coils, I would put those at the top of my list to check. They are notorious on these bikes for taking a dump.