90 Evinrude 1981 cylinder missing

[RobertSS]

Owned motor since new, 15 years ago one cylinder would just suddenly stop firing while cruising along. 2-3 mins later it would fire up again like someone turned a switch on. Would happen only once or twice a season. Last year started happening every run. Took to shop and replaced 2 coils and power pack on one side and new timer base. Ran beautifully! This season motor starts only on 3 cylinders each day. Run for 15-30 mins like that pulling kids on tube (barely!) and all of a sudden, like someone flipped a switch, the 4th cylinder fires and it’s fine the rest of the day. Multiple starts that day and all cylinders fire no problem. Start motor next day and all cylinders fire beautifully. Leave the motor for a couple days though, and I’m back to only 3 cylinders firing. Driving me crazy. What do you think I should look at?

 

[racerone]

Replaced plug wires?----Could be shorting to the cowling.

 

[RobertSS]

Good idea. I have moved the dead cylinder plug wire around many times, trying to change how it rests again supports, etc. but doesn’t seem to make a difference when I start it up. Are those special wires or can I use some standard plug wire and make a new one?

 

[racerone]

Solid wire core.----Perhaps new boots on the ends.-----Start and test running with cowling off can be done too.

 

[RobertSS]

Thank-you. I shall try and see what happens.

 

[boobie]

Do you know which cylinder is causing the problem ??

 

[MTboatguy]

You do have a spark tester don't you?

 

[RobertSS]

Bottom cylinder on port side. No spark tester so I used an inductive pickup timing light.

 

[MTboatguy]

My inductive timing light has never been reliable on my boat motors, which is why I always have a spark tester on hand when troubleshooting a boat motor, they have a decent one you can pick up at HF for about $5

 

[Bosunsmate]

Clean the grounds to it, right into the bolt threads/grooves

 

[RobertSS]

Spark tester proper and cleaning grounds...check. Will try that next week when I’m back. Which ‘ground’ bolts would be the ones I should key in on?

 

[Bosunsmate]

Spark tester proper and cleaning grounds...check. Will try that next week when I’m back. Which ‘ground’ bolts would be the ones I should key in on?

Any from the coil or powerpack
Some coils have the fixture bolt also acting as the ground. The threads on the engine side can get electrolysis/corrosion in them