New Old Stock carb

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  • August 24, 2024 at 8:18 pm #290168
    robotmark
    Participant

      Hi crew! Today I got a “new” old stock carburetor for my ’71 40 hp Johnson. It was in its original box and very clean, but it’s still be sitting around for 40+ years. Are there any recommended steps before putting on my engine and firing it up? Thanks!

      August 25, 2024 at 5:18 am #290169
      aquasonic
      Participant

        US Member

        The original cork floats were coated with shellac which is not very resistant to ethanol. The newer floats are made of ethanol resistant plastic.

        The original black main gasket has been updated to a tan nitrile gasket in the OMC kits. Not sure about the ethanol resistance comparison. Sometimes the black gaskets are degraded and cracking.

        It seems like the nozzle gasket is now made out of nitrile. The original ones tended to crumble.

        If you plan to use the motor on a regular basis, a new OMC carburetor kit would be a good upgrade. Avoid the cheap aftermarket kits they have a host of problems.

        August 25, 2024 at 10:31 am #290173
        frankr
        Participant

          US Member

          Yeah, go back old enough and they did have shellac coated cork floats.  But 1971 should have what looks like shellac coated floats but are alcohol resistant.

          August 25, 2024 at 12:17 pm #290178
          robotmark
          Participant

            It’s interesting. I’ve had good luck with the cork floats, as opposed to the black plastic ones that come in the new kits. The cork ones I have haven’t really degraded and seem to fit a little better. Now that I’ve got two carbs, maybe I can do an A / B test to see what kinds of differences I see. After digging around it seems that the carb assembly was from 1983.

            August 26, 2024 at 1:23 pm #290205
            robotmark
            Participant

              OK – so I cleaned the carb, installed it, and seated the needles at the recommended amount of turns. I took it out on the reservoir today and it fired up immediately. However, as you can see in the video I linked, at WOT I only went about 6 mph (on a good day I can hit 28 mph with this thing). Any thoughts on where I should look first to figure out why I’m bogged down at WOT?

              https://youtube.com/shorts/yOpxjmY5EnM

              August 26, 2024 at 1:52 pm #290206
              aquasonic
              Participant

                US Member

                I can’t watch the video because it’s “private” and the viewer needs to sign in.

                Anyway, did you adjust the high and low speed needles on the boat? Are you getting spark to both cylinders? Are you sure that the NOS carburetor is correct for your motor?

                August 26, 2024 at 2:03 pm #290207
                robotmark
                Participant

                  Try this link (it hadn’t finished publishing yet) https://www.youtube.com/shorts/yOpxjmY5EnM

                  So yes, I adjusted both needles on the engine while under power. It was idling beautifully and when I adjusted the high speed it sounded like it was going fast but the boat was going relatively slow. I can run by spark plug tester today, but I’m pretty sure they were both firing. And finally, the NOS carb is identical to the one that was previously on there (OMC model 384919). 

                   

                  Thanks!

                  August 26, 2024 at 5:21 pm #290210
                  Buccaneer
                  Participant

                    US Member

                    If the cables are adjusted to let the throttle open all the way,
                    then back to the basics.

                    Prepare to be boarded!

                    August 27, 2024 at 10:38 am #290228
                    bob-d
                    Participant

                      US Member

                      Double check the plugs to see if it’s firing. Those big twins can idle very nicely on one cylinder. Had same problem this summer, one brand new Champion was bad.

                      Bob D

                      August 27, 2024 at 2:17 pm #290232
                      aquasonic
                      Participant

                        US Member

                        I watched the video, and the motor does not sound like it’s getting up to the proper RPM. It may well be running on one cylinder as bob-d mentioned. The symptoms fit.

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