1974 15hp johnson running on 1 1/2 cyl

[Wavecharmer]

I have a 1974 15 hp Johnson that looks like it just stepped out of a time machine, that being said it has a problem. At slow speeds its missing on one cyl also starts hard inconsistently. Sometimes one pull and your off, the next time five pulls and your flooded. Runs great at top end plenty of power.
Took motor to local mech he changed lower cank seal, exhaust rubber mounts and spent two weeks with it and gave up. I suspect its electrical but what. Has spark, compession 118 per cyl. Driver coil? Ive heard ignition coils work or they dont. not inconsistently.

[boats.net]

Did the mechanic clean carb? check ignition to see if it is dropping fire on a cylinder?