Re: powerpac ?
In your case, a failed powerpack isn't likely. I've yet to see one of those type packs to be intermitent. It's always been a case whre if the pack was bad, it stays that way.
Are you using Champion QL77JC4 plugs gapped at .040 ? If not, do so and if you're lucky, that might cure the problem.
Also.... if you have a tachometer and it's been acting up or not working at all, possibly the rectifier has failed for some reason. This would allow voltage to back up at the stator (beginning of charging and ignition system) which would cause the stator to overheat and start to melt down. This in turn would result in a voltage drop from the stator to the powerpack..... resulting in weak, erratic, and evntually no ignition (spark).
Check that stator (under the flywheel) to see if there's a substance dripping down on the timer base and powerhead area, and if so, replace the stator.