Mysterious missing/shaking 1994 Johnson 140

So I have been searching all over and not found any similar issues from others.

I have a 1994 Johnson 140, and it has performed relatively well for me in the past, I have had a rattle of the front latch that I was finally able to resolve by wedging a roll of tape between it and the case.

So on rare occasions I have taken off pulling a wakeboarded or not, but probably immediate push of 3/4 throttle and it has just lost power or cut out, no change in throttle and it clears and goes, as I said rare and so out of sight out of mind, but it has occurred.

Now I went out last weekend and everything was great, except between 4000 and 4500 rpm, engine would either miss or something else cause boat to shake some and could hear an audible miss. If I gave more throttle it would come out of this situation and be nice and smooth as I have experienced in the past. At one point the issue seemed to pop up at lower RPM but I was not able to reproduce. Just got very concerned that I was far from the trailer and not looking forward to a long slow ride home. I finished the day running just up around 4000 smoothly and got home safe.

I also noticed when I powered up at one time during testing the range it jumped very quickly to 5000.

So might anyone have any suggestions or ideas? I don't but figured I would run an Engine Tuner and hope it helps.

Tony

Re: Mysterious missing/shaking 1994 Johnson 140

I would be looking for a bad plug, old plug wires or spark jumping from plug wires to the cowl latches.

Re: Mysterious missing/shaking 1994 Johnson 140

Ok, I will look into that. What about coils? I did have a mechanic work on it at one point and they indicated some issue with one or more of the coils, not that they were not functioning but more regarding age and they had trouble making some connections. I don't recall why they did not replace what needed replacing, but kind of a impression they did not want to so they could avoid breaking mounting bolts, etc. I doubt I will ever take my boat to them again if it goes to a mechanic.
Tony

Re: Mysterious missing/shaking 1994 Johnson 140

I think what you have is a cylinder not firing under load. 4000+ must be enough of a different load that it causes failure. Check the easy stuff first (like plugs and old wires). Then, do a proper spark check with the correct air gap.

New coils wouldn't hurt either, but maybe not necessary. Not sure how you tell if one of those 90s coils (sealed black plastic) is old.