Pull the flywheel off using a flywheel puller. DO NOT undo all the bolts at the hub! You may need to remove two bolts to use a harmonic balancer puller. I can't recall if Mercury had the threaded hub on those yet. In any case, start with cleaning the points and gapping them at .018". Failing that, if the coils appear good, they likely are. Condensers can be a weak spot on those, too. Check plug wires for cracking.
