1956 Johnson 10hp bogging under throttle

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  • September 7, 2016 at 8:26 pm #5194
    gabriel
    Participant

      I finally got my motor running so I put in on the boat for the first time this past weekend. The new gear case I installed shifts fine, and after re-threading one of the spark plug holes the motor started up pretty quickly. I’ve got it to a point where it cold starts within 3-5 pulls and once warm starts very easily. Pumps lots of water and idles okay (carb set to factory settings).

      Before I go further I’ll mention that I was running it without the shift rod cover plate (lost it). I’m hoping I’m just stupid and this is the source of my problems. I wasn’t sure if this was necessary for proper exhaust back pressure.

      Basically, the motor doesn’t seem to have the power it should. At 1/2 throttle it barely pushes the 12ft aluminum boat 5mph. When I go above 3/4 throttle it revs erratically and makes a whining sound, at one point it sputtered out and died.

      From what I understand it could be running on one cylinder. Is it also possible the prop is rubbing something it shouldn’t or I have some gear case damage? I’ll admit I haven’t really checked the compression or the ignition system as I don’t have the tools to do so, although it has the newer black coils and seems to be in good condition. I cleaned out the carb but didn’t change any gaskets. I also redid the pressure tank seals, fuel connector orings, and new fuel lines.

      Let me know your thoughts.

      Thanks

      September 7, 2016 at 9:01 pm #43551
      chris-p
      Participant

        Sounds to me like the prop hub is spun, to test use a sharpie and make a mark across the hub to prop. run it till it revs up, then check mark. If now askew, the hub is spun. Or, try another prop.

        If not that, ensure running on both cylinders.

        September 7, 2016 at 9:19 pm #43552
        frankr
        Participant

          Whining is often caused by worn bushings in the lower unit, which throw the gears out of alignment. OR, something holding the drive shaft down (it needs to be allowed to float upward slightly under power).

          September 7, 2016 at 10:48 pm #43555
          fleetwin
          Participant

            US Member

            Could be something as simple as the prop hub, or it could be that you have more than one problem. I’m assuming you checked/changed the gear lube and the gearcase wasn’t full of water. Are you sure the shift linkage is adjusted properly? It is easy to misalign that shift rod connector and strip the clamp screws, causing the engine to jump out of gear. I don’t think the missing shift rod cover can have much of an effect, except for a big exhaust leak/noise. I suppose it is possible that the engine is breathing its own exhaust, but not real likely.
            The engine might be running on one cylinder, I don’t know what would cause it to sputter and die.
            It would be helpful if you could post a video of the engine running/misbehaving.

            September 8, 2016 at 4:16 pm #43625
            outbdnut2
            Participant

              US Member

              If it was just sputtering and dieing when you open it up, I’d be suspicious of a bad or missing donut seal washer between the carb float bowl and the venture tube coming down through the center of the float, making it flood, but this will not make it whine. I’d be suspicious of BOTH a carb problem and the prop hub letting go under load.
              Dave

              September 11, 2016 at 12:26 am #43758
              gabriel
              Participant

                Well I took off the prop and found a few metal shavings so I think it was spun. I put a different prop on and checked it was running on both cylinders.

                Went for a test run, there was no whine and it went up to WOT smoothly, pushing the boat pretty good. However, when I would lower the throttle from full to 3/4-1/2 it sputters out and dies. Then it takes 15ish pulls to start again.

                What I don’t understand is before I took the motor up to high speeds it would start very easily. This was all on factory carb settings.

                Thinking I should probably get a carb kit and float.

                September 11, 2016 at 12:40 am #43760
                frankr
                Participant

                  I don’t know what you are calling "factory carb settings" If you are meaning the preliminary settings, they are just that–preliminary. They need to be fine tuned on a boat, on the lake for optimum performance.

                  September 11, 2016 at 12:46 am #43761
                  frankr
                  Participant

                    Reading your story again, I don’t see any mention of having checked the ignition system. Your statement about sputtering and dies, then pulling it 15 pulls when warm is the classic symptom of bad coils. Unless they have already been replaced, ALL 1956 Johnsons have bad (cracked) coils.

                    September 11, 2016 at 3:13 am #43777
                    gabriel
                    Participant
                      quote FrankR:

                      I don’t know what you are calling "factory carb settings" If you are meaning the preliminary settings, they are just that–preliminary. They need to be fine tuned on a boat, on the lake for optimum performance.

                      Yes, I realize that carburetors require adjustment. I only mention this to clarify that I don’t have it set completely off, nor have I fine tuned it yet.

                      September 11, 2016 at 3:18 am #43778
                      gabriel
                      Participant
                        quote FrankR:

                        Reading your story again, I don’t see any mention of having checked the ignition system. Your statement about sputtering and dies, then pulling it 15 pulls when warm is the classic symptom of bad coils. Unless they have already been replaced, ALL 1956 Johnsons have bad (cracked) coils.

                        The thing is it has the newer black coils that are not cracked. I believe a tune up was done 30 years ago but I do not know the extensiveness.

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