Hummm, always interesting to see us amateur mechanics voicing our opinions, so let me not be stifled,,,
I’ll bet an extra thick frappe from Sawyers that its either the ignition coil or if it’s a Mercruiser then possibly the distributor module.
My argument would be that if its running good at any point its probably not any of the other items discussed.
Seems to me like a classic ignition coil problem, but having had those crappy Mercruiser distributer modules burn out, I wont rule that out.
That said, some of the checks suggested are easy enough to work through and eliminate. Re-checking the firing order, checking the condition of the plug wires, unscrewing the gas cap, and replacing the fuel with known/new good gas are all easy and sensible things to do and probably should try.
But I’m sticking to my prediction and I don’t give up my Sawyers coffee frappe without a fight, so I look forward to the outcome.
Best of luck.
