1953 Big Twin Fires on Two but Runs on One Cylinder Only

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  • June 5, 2019 at 7:35 am #176654
    Jonathan Dower
    Participant

      Fleetwin…thanks for comments. I was nervous about removing the reed plate,but, on the chance that the top cylinder valve wasn’t closing properly, I swapped the bottom cylinder valve with the top: no change…the top still wasn’t igniting.

      The motor ran fine last summer, until late in the season when it became hard to start and would run only with the choke open…and poorly then. Carb was rebuilt over the winter.

      I have used the inline spark tester, running at both idle and as high a speed as I can get it in a barrel. The spark seems to be the same on both cylinders.

      As I mentioned in my initial post, there was some oil under the magneto plate which I cleaned before replacing points. Would a bad upper seal present these symptoms?

      Thanks again

      October 27, 2020 at 11:18 am #219419
      The red boat
      Participant

        Jonathan

        did you ever figure out what was up with your motor?
        I’m running into a similar situation with my ’55 Evinrude 25hp except my problem cylinder is the bottom cylinder.

        October 27, 2020 at 11:55 am #219422
        Mumbles
        Participant

          Oil under the mag plate is usually a sign of the upper crank seal leaking. The O ring inside the carbon is probably dried out and brittle allowing fuel mix out and air in. The joint between the two crankcase halves could be leaking to.

          October 27, 2020 at 12:01 pm #219423
          crosbyman
          Participant

            Canada Member

            ……Plugs are wet, but seems to be gas well is it pure gas& oil … will it burn with a match or is it wet with water ??? there again water would probably pearl

            what ohms do you see on both plug boots to frame while upping the throttle from slow to fast are wires all new metallic

            Joining AOMCI has priviledges 🙂

            • This reply was modified 5 years ago by crosbyman.
            October 27, 2020 at 7:00 pm #219461
            fleetwin
            Participant

              US Member

              Like I said, pulling that exhaust cover can be a messy job, I would hate for you to do that based on our guess…So, how about removing the gearcase so the water pump won’t be damaged, then starting the engine to see if it runs on two cylinders with no water going through the powerhead….
              And, just to confirm your findings, you could always hook up a water hose to the water tube. Start the engine with no water going through, if it seems to run on two cylinders turn on the water hose, it should drop back down to one cylinder if water intrusion is an issue…

              October 27, 2020 at 8:02 pm #219464
              dave-bernard
              Participant

                US Member

                water would steam clean the cyl.

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