Engine problem - '85 Mercruiser 170

[scook]

I got their flame thrower coil with it and cut out the resister wire. I've got 12 V plus. I read Spare's suggestion that I should check it right when it pooped out to be sure something wasn't changing as a result of operating the engine - temperature or some other cause. Intuitively, I don't see what would cause the voltage to drop and if it did, would it cause RPMs to decrease as opposed to just dropping off suddenly,to zero. Of course, my intuition hasn't got the problem fixed either.