1954 Johnson RD15A Spark advance at startup

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  • December 31, 2020 at 4:25 pm #226645
    olcah
    Participant

      US Member

      This motor starts at a low speed. Almost an idle which makes makes manual starting difficult. The photo shows the magneto idle stop against the gearshift detent lever with the tiller handle in the start position. I am so tempted to file off about 1/8 inch off the end of the idle stop to advance the magneto and hopefully raise the motor rpm on startup.

      But before I do, does anyone have any advice whether to do or not do this mod?

      Wishing everyone a happier and healthier New Year.

      100_6749

      December 31, 2020 at 5:52 pm #226660
      Buccaneer
      Participant

        US Member

        Is the cam synced to the carb correctly?

        Prepare to be boarded!

        December 31, 2020 at 6:08 pm #226661
        crosbyman
        Participant

          Canada Member

          see pages 154 155

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          December 31, 2020 at 7:02 pm #226667
          olcah
          Participant

            US Member

            Buc and Crosbyman, Yes the carb and plate are in sync. Appreciate the page enclosure . I will print it off as that in my copied manual is hard to read. I also have a 1954 Evinrude 25 hp and it has a similar problem with slow speed on starting but it is also in sync.

            December 31, 2020 at 7:21 pm #226668
            crosbyman
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              Canada Member

              see my PM

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              December 31, 2020 at 7:43 pm #226673
              crosbyman
              Participant

                Canada Member

                better find the problem instead of modifying the hardware…

                compression ok ? carb idle chamber clean ? sparks ok ? points …condensers ok ? see the coils ok from boots to engine frame with a ohm meter ?

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                January 1, 2021 at 2:27 am #226679
                olcah
                Participant

                  US Member

                  Crosbyman, I am unfamiliar with the term “carb Idle chamber” can you explain?
                  Thank you.

                  January 1, 2021 at 9:51 am #226684
                  crosbyman
                  Participant

                    Canada Member

                    these older carb all have a small vaporizing chamber in the idle circuit. fuel goes up the side of the carb thanks to the crankcase vacum then goes into the small chamber via the pointy LS needle.

                    the fuel then gets sucked in the crankcase . this becomes the main source of fuel at start up. As the throttle opens up the high speed circuit takes over and less and less fuel comes from the low speed circuit

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                    • This reply was modified 4 years, 6 months ago by crosbyman.
                    January 1, 2021 at 10:02 am #226687
                    crosbyman
                    Participant

                      Canada Member

                      see carb flow description page 101

                      jw cd ad rd basically work the same except that some types have adj. needles ….on both LS and HS

                      other models have fix jets mostly on the HS side of the carb

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                      • This reply was modified 4 years, 6 months ago by crosbyman.
                      January 1, 2021 at 10:18 am #226690
                      olcah
                      Participant

                        US Member

                        Crosbyman,
                        Thanks for the great info. Never noticed it in the manual. I will take the carb off and check that it is clean in that area.
                        Wires were replaced last year. I had spark on both cylinders jumping a 1/4 ” gap tester a couple of days ago. I will try to get a compression reading. Difficult to get an accurate compression test as the stand is shaky and motor is manual start. Compression was top 94, bottom 89 in October 2019 with very little running since then.
                        Apprecate your advice.

                        Edit correction – compression readings in Ocotber 2019 were top 94, bottom 89.

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