Intermittent fire on one cylinder.

[wvmedic]

I have a 1973 50 HP Evinrude model 50373R, and it has intermittent fire on one cylinder.

I have rebuilt the carbs, compression is 120 Psi top cylinder 118 on bottom cylinder.

The problem started with the motor not idling unless the high idle lever is up, so I did a link and sync and it was ok.

Did a spark check got good 7/16 th. Spark from both coils but the bottom coil would drop the spark about every 3 to 4 seconds. I then switched the wires around on the power pack and both coils were now not firing right, I know now that was not the right thing to do. But I put a new power pack on and still had the same problem, so I moved the coils and the problem followed the coil from the bottom cylinder to the top. Ok so now that suggests that the coil was bad, I replaced it with a new coil and still had the same problem. I then moved the coils again and the problem followed the new coil, I tried different coils and still the same problem.

I rented a DVA meter and got .78v on the trigger and 220v on the stator. I then checked the trigger wires separately to the engine ground and got 35.4v multiple times on the whit/black wire I think I got 150v twice on that but it was pretty consistent at 35.4v.

The black/white wire produced a consistent 220v. And the output from the power pack was 180v to 190v.

Any ideas as to what the problem is, do I have a bad trigger?

Thanks Jeff.

 

[wvmedic]

Re: Intermittent fire on one cylinder.

I updated the post because, I had the stator and trigger names reversed.

Jeff.

 

[wvmedic]

Re: Intermittent fire on one cylinder.

Please can anyone offer any info to help me with this problem?

Jeff.

 

[wvmedic]

Re: Intermittent fire on one cylinder.

Well I decided to go over every piece of wiring on the motor again today. I found a small hole in the insulation of a red power wire at the plug coming from the control unit, it was held to the block with a wire holder and I believe it was grounding out. We taped it up and let it stay loose away from the block, the motor now idles and will plane out.

Man what a nightmare that was to track down.

Jeff.

 

[ondarvr]

Re: Intermittent fire on one cylinder.

Its good to see you got it figured out, and without help too. You did exactly what would have been recommended, so good job. Sorry you didn't get any responses though, sometimes it gets so busy here in the spring people miss a a thread and it gets lost.

 

[wvmedic]

Re: Intermittent fire on one cylinder.

ondarvr thanks for the reply, I am just glad to have finally figured it out.

This motor was driving me crazy, all though that would be a short trip.

Jeff.