skipping

Sorry for the long story Hi guys new to boats and posting. Trying to grasp this internet thing. Given a 95 sea ray which sat for 10 years. So I first Emptied fuel tank. Sloshed with small amount of fuel and emptied. I then filled tank with new premium fuel and added sea foam. Changed the plugs...

I have a 1999 210 bow rider with a 5.0L Mercruiser EFI. Just recently I have had some trouble starting it, and, more of a problem, once it has been running a while the tachometer goes crazy, bouncing between zero and 5000 rpm while the engine skips and pops. It sounds like the coil to me, but...