Re: 50 HP merc 5oo
I blew a coil on my '77 and had no spark at all on #3. I'm confused at your description, are you saying that you have spark on 1-2-3-4 but #4 is missing and cutting out occasionally?
Have you metered your coils? Disconnect your plugs, measure plug wire to ground and then primary screw to ground, be sure they are all about the same. You may even want to swap your coils around and see if it follows. The insulation on a coil can break down internally or even get a pinhole in the outer skin and it will arc. On mine, some idiot broke one of my plug wires at a shop. that energy has to go somewhere, if not to a plug, it will find ground even if out the side of the coil.
