I have a '96 Nitro with a 75hp, 3 cyl Mercury on it; owned it for around 12 years now; always winterized and Stabil Marine used in every fill up; always ran great until this year when an issue started. The issue is that when I go to get on plane and start to give it throttle, it cuts back to 2 cyl (starts missing a cyl).
Some details:
---it only does it after its warmed up and been running a while
---I replaced plugs and wires=no change
---I then replaced fuel filter and rebuilt the fuel pump=no change
---It's such a sharp cut-out that it really feels like spark to me, not a fuel issue
---today when it did it I checked the primer bulb and it was full and hard
So, recap, after its hot and I go to get on pad, I get around 3/4 throttle and it starts missing a cylinder. I can back off the gas and it will pick back up and run on all 3 cyl until I goose it again, then it loses a cylinder again. I know this makes it sound like a fuel delivery problem but I really think it's spark. And if I just run it at around 1/2 throttle, it stays fine, only does it when it starts to rev.
For what its worth, the tach has never worked correctly on this boat since I got it. It always gives screwy readings. But it's done this since I got it and it's always run fine; probably just coincidental; not sure where the tach reading is taken from.
Any and all ideas are welcome.