Home Forum Ask A Member 35 hp Johnson carb tuning question

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  • #1537
    boatman
    Participant

      Hi all,

      Finished a carb rebuild on a ’59 Johnson 35 hp with a OMC rebuild kit, also did new fuel pump diaphram. Idles well, and will run well wide open, but getting to wide open is an issue. From 1/4 to 3/4 throttle the motor surges and acts like it wants to go, but continues to stutter and surge for 30-45 seconds before finally taking off and going like hell at full throttle. Runs beautifully once it is going at wide open. I can decrease throttle to 3/4 without losing power, but below that the surging/stumbling returns until I get to idle speed. Have set the needles at 3/4 and 1 1/2 turns from seated.

      I assume it’s a fuel delivery problem, but I thought I cleaned all passages well when rebuilding the carb. Any thoughts? Appreciate the help. Hoping to get my daughter and my nephew out on the tube and maybe skis for the first time this weekend.

      Thank you,
      Paul

      #16443
      fleetwin
      Participant

        US Member - 2 Years

        Well, you may want to check carb synchronization first. The economizer linkage/rod may be out of adjustment also.

        #16456
        boatman
        Participant

          fleetwin,
          Thanks, I will check that out.
          Paul

          #16478
          chris-p
          Participant

            Did you istall the gasket/o ring around the nozzle, which runs up through the cut out of the float?

            #16487
            necks
            Participant

              US Member

              Boatman, It sounds to me like the carb is adjusted to lean. If you got the motor to idle nice by adjusting it out, when you hit throttle to full throttle and it bogs out, bring throttle back to idle and adjust, turn idle adjustment screw to the left (richen) 1/8 turn at a time. Advance throttle to full throttle to see if it still bogs down. If it still bogs down repeat procedure. Idle circuit should run a little rich. Also when adjusting carb the motor must be in forward gear.

              #16493
              vintin
              Participant

                I’ve found with my 1957 35hp RDE that if the idle is set lean enough to not have some mid speed over richness…and a miss……that it suffers from cold lean sneezes. After the engine has warmed up the lean sneeze at idle goes away. With a cold start with me sitting at the motor giving it half choke after starting it eliminates the cold lean sneeze.

                After getting your 35hp warmed up have somebody else drive and have them give it good throttle from a dead stop. If you get missing lean up the idle a little and try it again. Alternately, from a dead stop giving it good throttle if you get missing give the idle needle a good twist towards leaner side. You might be surprised and find that your missing or bogging is from the carb running a little fat in it’s mid range until the butterfly opens bringing the high speed jet into play. I did.

                Then adjust the high speed needle following standard protocol.

                Then fool with the low speed settings.

                I’ve found that I can get a good non sneezing cold start if I fatten up the low speed jet about two numbers. Then of course it needs to be leaned out two numbers after warm up. This will wear out the packing washers fairly quickly.

                It would be nice if these motors had a continually adjustable remote choke, but they don’t.

                Do make sure as was mentioned earlier that the transition point where the high speed jet joins the low speed jet output is set correctly (carb synchronization). Ditto for the economizer adjustment. If you don’t know what these are, you’re going to have to know if you want your motor to run at it’s best.

                Also see the thread on the use of a timing fixture on these motors.

                When it all comes together these are beautifully running motors.

                Is your motor passing good water flow?

                #16495
                raglover
                Participant

                  I always tweak mine when going out the first time. My wife or friend at the controls cover off. Get it idling in fwd gear and richen the low speed needle until I get it slw enough to set docking speed without dying

                  Then get them to go full throttle in a controlled but steady pace and tun in the high speed until I hit max rpms possible and highest speed the go back rich 1/8 to 1/4 turn to make sure I am not too lean.

                  Take your 7/16 wrench to loose. The packing nut while adjusting the cinch it down once you have it right.

                  Mine will big at midrange until it get it dialed in after storage.

                  #16498
                  boatman
                  Participant

                    Chris,
                    I’m sure I did, but will take it apart for a clean up after sitting through the winter. I did not check the synchronization, so will check that out.
                    Thanks guys for the other tips as well.
                    Paul

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