1984 or 1985 115 hp Merc. 6 cyl. outboard. I was in Canada for week fishing trip the first problem it started knocking some where on the top end of the motor got it back to the dock, it sat over night problem was gone in the morning, next day again latter in the afternoon it started knocking again then quit, but on the way back to the cabin it died out, I could get it started but it would not get up on plane, it would start missing and almost die out, but run smooth at idle and no knocking, we idled all the way back to the cabin, pulled it out in the morning took it to the local marina checked out a few things tried a new set of spark plugs but same thing, so we decided it was a bad switch box (power pack) these motors have 2 each runs 3 cylinders. The guy at the marina had a good used one it was a crap shoot so I replaced the bottom switch box put it back in the lake problem solved it now runs good gets on plane good all is good. We figured the knocking was detonation, a cylinder trying to spark at the wrong time. So the next day we head out get out on the lake about 5 miles and starts acting up again, this time the miss starts happening at around 4,000 rpm it starts cutting out, if I run it below 4,000 rpm it is ok, not a big deal we just ran it the last 2 days of our trip below 4,000 rpm. It gets up on plane fine and runs good untill 4,000 rpm. So could it be bad spark plug wires? another bad switch box? We did test the high speed windings of the stator there seemed to be no short. Any other idea's anyone? BTW the miss definitely sounds electrical.
Last edited: