1956 Johnson 30hp High Speed Tuning

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  • July 18, 2022 at 12:50 pm #263138
    rhalbert10@outlook.com
    Participant

      US Member

      Thanks for the very good info above.  Here is the update from my runs yesterday:

      • I cut down the fuel line by 4 1/2 feet – it was way too long in the well anyway and kind of drove me crazy…
      • I added some Sea Foam engine cleaner to the gas tank just to rule some gunk in there that may be causing issues.
      • Was able to run almost indefinitely at 19-21 MPH and definitely a bit longer at 25 MPH but it still would crap out eventually – especially if I hit wakes hard which is a behavior that I find very strange.
      • I had my dad drive and I sat in the back with the motor.  If I occasionally pumped the fuel bulb we never had an issue and could maintain speed.
      • That led me to the fuel pump does not have the proper throughput to hang at full throttle. That appears to mirror what you all are saying as well…

      As far as replacing the fuel pump (the suggestion above was with the Sierra 18-7351) does that unit truly fit the 30HP motor as when I go search that on the web it mentions 9.9HP or 15HP engines.  Just don’t want to get under powered again.  And is this a fairly simple swap out of what I have already.  Having trouble completely visualizing this one installed.

      Thanks again to everyone – this info is invaluable!!

      Rich

      July 18, 2022 at 1:10 pm #263139
      frankr
      Participant

        Hi Rich.  OK, I’ll confess I haven’t torn one of the 7351 pumps apart recently.  Who knows, they might have cheapened that one too.    But I’m confident it will fit your motor.  Some hose re-routing will obviously be needed.  And it will pump plenty of fuel for your 30hp——IF they haven’t screwed up the design inside of it.

        July 18, 2022 at 1:24 pm #263140
        frankr
        Participant

          Repair kit 18-7800 for 18-7351 still looks good.  I don’t see any flapper valves in it.

           

          18-7800

          July 18, 2022 at 2:05 pm #263144
          rhalbert10@outlook.com
          Participant

            US Member

            Order placed…thanks for the help  Will report back once I get it replaced.


            @frankr             – where did the diagram come from for the “good” and “bad” versions of the OEM fuel pumps?

            July 18, 2022 at 3:29 pm #263145
            frankr
            Participant

              1961 OMC/Gale parts book.  Johnson & Evinrude used the same pump in their “Cruiser” fuel system.

              July 18, 2022 at 5:05 pm #263153
              Don
              Participant

                US Member

                I keyed in on your comment about the engine running poorly if cruising in choppy water, am I hearing you correctly? Some of these carbs never used the big old nozzle gasket, don’t know why. Perhaps the fuel is slopping around in there, dumping inside the nozzle well causing it to run rich. Just a “guess”. Any way of providing a video of the engine running/misbehaving?

                July 22, 2022 at 3:49 pm #263426
                rhalbert10@outlook.com
                Participant

                  US Member

                  Post modification report:  TOTAL VICTORY!!!!

                  Changed the fuel pump with the Sierra 18-7351 and took it out today.  It worked perfectly.  Absolutely zero issue at all speeds.  Help top speed as long as I wanted to go and even sounded better from idle to max.  Amazing result for $60 if you ask me.

                  Many thanks to this forum and @frankr for all the great advice.  Pictures below of the install.

                  Happy boating (finally!!)

                  Rich

                  July 22, 2022 at 5:33 pm #263437
                  BRUCE REINHART
                  Participant

                    Canada Member

                    Another thing I would do is drop the sediment bowl on the carb and take out the filter cartridge , put the bowl back on and take it for a run at full throttle , I have had older snowmobiles that had the same  symptoms and ran great after a new filter was installed  , just another look at it

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