1939 Neptune 2A39 Won’t Keep Running

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  • May 30, 2015 at 8:04 pm #1639
    lightfoot
    Participant

      This is a 1939 2A39 2 hp Neptune with the original Tillotson MS-105A carburetor. I can only get it to run for about 2 or 3 seconds. It seems like it isn’t getting enough gas, but I’ve had both jets opened in small increments from 1 turn all the way to 4. Nothing seems to make any difference. The best run was while playing with the choke once after it started. It may have ran about 5 seconds and then died. Prior to these tests, I took the carb apart and soaked everything in a can of Chem-dip Carburetor Cleaner for 24 hours and then blew everything out. I’m using fresh 16/1 gas/oil in a jury rigged clean gas tank. All the lines are clean. After a frustrating day I dismantled the carb again to look for debris but everything is clean. It’s fairly easy to start, and I must have started it at least 40 or 50 times while adjusting the carburetor.

      One thing I did find when I initially took the carb apart was the bottom jet looks like my dad stripped the screwdriver slot trying to remove it so I wasn’t able to remove it during the Chem-dip cleaning. The needle looks ok, and I can’t see any damage to the hole, but I think that jet needs to be replaced.

      Suggestions???

      May 30, 2015 at 9:00 pm #17223
      RICHARD A. WHITE
      Participant

        Lifetime Member

        Your tank height should be ABOVE the carb….easy thing to miss…also can you see the float needle rise? I think that has one of those….If it has no float needle, take the top off the carb and open the fuel valve, float better rise…lol

        http://www.richardsoutboardtools.com
        classicomctools@gmail.com

        May 31, 2015 at 12:20 am #17242
        lightfoot
        Participant

          I have the original tank off for cleaning. My jury-rigged tank consists of a 5 foot clear plastic tube filled with pre-mix and suspended above the motor. This way I can see the fuel going down and refill as necessary. It’s connected directly to the copper feed tube that connects the original tank to the carburetor. Yes I cleaned the copper tube and the plastic tube prior to starting the motor. The float needle and float work fine and are clean. Everything is clean. These carburetors are about as simple as they come so I’m not sure why I can’t keep the motor running. As I said, the only defect I can find is the screwdriver slot in the bottom jet is stripped so the jet can’t be removed. However the needle and the hole in the jet look fine. Obviously something had caused my dad to try to remove the jet but he wasn’t able to get it out. I have great memories of running around Center Lake in the township of Camp lake Wisconsin with my father running that little Neptune when I was young. Sometime around 1957 he upgraded to a 5 hp Johnson and stopped using the Neptune. That’s the last time this thing ran. I was 11 years old then. It would be great to bring this thing back to life if someone can help me figure out whats wrong, or may be wrong. Thanks for the suggestions about the float and gas tank but that doesn’t seem to be the issue.

          May 31, 2015 at 4:18 am #17266
          Doug Wilson
          Participant

            US Member - 2 Years

            is there a way to run a fine wire through that jet other option get some gumout and spray through the passages an make sure it gets through the passages in the carb could be soaking it loosened it but did not clear it. If you can find a replacement jet an easy out might break it free but no saving it at that point.

            Doug

            how is it motors multiply when the garage lights get
            turned off?

            May 31, 2015 at 5:21 am #17270
            slim60
            Participant

              If you think the carb is OK I would start by pouring some Seafoam into the cylinder to clean the gunk off the rings. Let it sit overnight. Maybe two nights. Mix some 8:1 gas. You can go back to 16:1 later. Remove the prop and muffler or exhaust tube. I just went through this routine with a ’41 opposed twin. You may have to spray fuel into the carb the first few times. When it runs let it warm up then shut it off to cool down. Do this five to ten times, then install exhaust. If it runs install prop. If not, go back. This is how it was explained to me. Your arm will get sore and this may take a few days, so good luck.

              May 31, 2015 at 6:53 pm #17294
              lightfoot
              Participant

                ddwilson, I’ll try poking a thin guitar wire through all the passages and jets, if that doesn’t work does anyone know what size the bottom jet is. My dad really tore it up trying to remove it so I won’t be able to read the size.

                Slim60, can’t do the Seafoam yet because I can’t keep it running longer than a few seconds. Funny thing is my left sholder hurt more from pushing on the cross handle to hold the motor still while pull starting with my right arm than my right arm did from pull starting. I must have started it about 50 times in one day.

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