1976 Johnson 35HP magneto problem

Home › Forum › Ask A Member › 1976 Johnson 35HP magneto problem

Viewing 10 posts - 1 through 10 (of 14 total)
1 2
  • Author
    Posts
  • August 8, 2016 at 4:14 pm #4943
    huppster
    Participant

      I can’t keep this engine running for more than 15 minutes without a misfire and dying. I’ve discovered that the spark jumps out of the boot on cylinder #1. As the engine warms up an passes 2000 RPM it gets a nasty misfire, keeps running on one cylinder and eventually dies. I’ve replaced points, condenser, plugs, driver coil, both plug coils and wires/boots. I’ve switched coils yet the issue remains with cylinder #1. Compression is 120 in both cylinders, reed vales look good and new fuel pump. Carb was also rebuilt. I purchased the OMC timing tool so I know the timing is right on. I can only think that as one of these components gets hot, that it fails but they all check out fine. I don’t have the proper equipment to test the condensers but I’ve replaced them twice. Any advice to help me diagnose this issue would be helpful.

      Attachments:

      August 8, 2016 at 5:13 pm #41764
      frankr
      Participant

        US MEMBER PAY BY CHECK

        The spark arcing out of the boot should be telling you something. In fact, the black tracks on the plug verify it. They should not be doing that. You say you replaced them? With OEM? Try some dielectric grease in them. Or get better boots.

        August 8, 2016 at 5:54 pm #41765
        huppster
        Participant

          They are new Sierra coils, should I just replace them with BRP coils?

          August 8, 2016 at 5:59 pm #41767
          fleetwin
          Participant

            US Member

            Do you still have the original coils? If so, I would test and try them instead. Perhaps there is a problem with the plug(s) causing the spark to seek an alternate path to ground. The correct Champion plug is the UL81C gapped at .030".

            August 8, 2016 at 8:18 pm #41775
            frankr
            Participant

              US MEMBER PAY BY CHECK
              quote huppster:

              They are new Sierra coils, should I just replace them with BRP coils?

              I see no reason to replace the coils (again). Get some OEM boots and just replace them. BTW, once they arc out awhile they probably will continue to arc out because the arcing creates a carbon path inside the boot.

              August 8, 2016 at 8:19 pm #41776
              fleetwin
              Participant

                US Member

                Very true….

                August 9, 2016 at 5:42 pm #41840
                PugetSoundBoater
                Participant

                  The path of least resistance is happening. I’d go with new correct plugs and clean the boots out well

                  "Some people want to know how a watch works, others just want to know what time it is"
                  Robbie Robertson

                  August 9, 2016 at 6:12 pm #41842
                  huppster
                  Participant

                    Thanks everyone for the advice – Ordered new boots and plugs today.

                    August 22, 2016 at 5:21 pm #42502
                    PugetSoundBoater
                    Participant

                      Was wondering how your ignition worked out after replacing the plugs and boots?
                      I had this same problem with the spark arcing on the outside of the plug on my 1976 9.9. Same scenario, all new ignition ,perfect timing. I cleaned the boot interior and the exterior of the plug well and retested. Was ok for awhile then started arcing along the outside again. I noticed that the trouble plug had its boot installed farther onto the plug compared to the other spark plug that was behaving itself. After cleaning the plug again I reinstalled the boot out a bit from its original position and it cured the problem. In addition to not using dielectric grease which would have helped,i think it was the terminal was closer to ground than the spark plug terminal,the spring terminal was installed a bit past the spark plug terminal itself ,and the spark would rather go the path of least resistance and distance than rather jump the gap.

                      "Some people want to know how a watch works, others just want to know what time it is"
                      Robbie Robertson

                      September 15, 2016 at 3:35 pm #44074
                      huppster
                      Participant

                        After replacing the spark plug wires and boots I also replaced the Sierra coils with OMC coils. So far it looks like the problem is resolved but I haven’t been able to run it under a load. I’m working on some lower unit issues. I hope to provide a full update soon.

                      • Author
                        Posts
                      Viewing 10 posts - 1 through 10 (of 14 total)
                      1 2
                      • You must be logged in to reply to this topic.