1957 Johnson 10 HP

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  • July 16, 2016 at 5:48 pm #4771
    mnmarty
    Participant

      I’m hoping someone has an answer to my problem.
      I have a 1957 10HP. I modified it years ago with the small Mikuni fuel pump. It has worked great for years.
      This summer it worked fine and then started to lose power at full throttle. I found if I kept working the primer bulb I could keep it going. The bulb was never soft, though. I really had to give it the extra squeeze. The hose and bulb are not new. They are old but I don’t see cracks in the bulb and it doesn’t get soft during running. When the motor would die I would inspect the glass bowl on the bottom of the carb. still full of gas.
      I ended up rebuilding the carb, buying new in line fuel filter, new plugs and a new diaphragm kit for the Mikuni. I even cleaned out the fuel tank since I could see debris in the bottom. There is new gas in it.
      I can start it up at the dock and if I keep squeezing the bulb every 1-2 seconds I can keep it running even at high idle. If I stop doing the bulb it will die.
      The only thing I haven’t replaced is the fuel lines and bulb. Oh and yes I even took the cap off the fuel can so there was no chance the vent wasn’t working. And I inspected the filter at the bottom of the fuel pickup. It’s clean.
      The motor runs smooth when I’m pumping it by hand.
      I have never put Sea Foam in gas tank.
      When I cleaned the tank I had pumped up the gas line and drained it by pressing the ball in the fitting. Gas squirted out under pressure.
      What am I missing? I’m totally stumped.

      July 16, 2016 at 5:57 pm #40329
      chris-p
      Participant

        Pull the hose off the carb and direct it into a jar while running. There should be a good stream of fuel flow. If not, go back to that pump, something is still not right. Where are you getting your pulse from, the bypass cover?

        July 16, 2016 at 6:56 pm #40330
        westwind
        Participant

          Canada Member

          I had a similar problem once. Turns out there was a kink in the hose to the carb restricting fuel flow. A little bit would get by at low speed but not enough for full throttle. Easy fix once I found it.

          July 16, 2016 at 7:32 pm #40332
          mnmarty
          Participant

            Pulse is from the bypass cover.
            I’ll try taking the hose off but not sure I can do it myself. I’ve got one hand working the bulb and don’t think I can pull it off the carb and do the test with one hand.
            I know the Mikuni are temperamental about how long the hose can be from the pump to the carb. If it’s too long there is too much resistance and not enough flow. The thing is, I haven’t changed anything. If the gas lines get older could they change their stretch and lead to more resistance?

            July 16, 2016 at 7:38 pm #40333
            dave-bernard
            Participant

              US Member

              O rings leaking on the hose????????? sucking Air.

              July 16, 2016 at 7:46 pm #40334
              chris-p
              Participant

                Sorry, let me re iterate.

                Prime up the carb bowl. Remove the fuel line, and run into a jar. Then start the motor and watch the flow. You will know if it is sufficient. The fuel in the bowl will let it run long enough to observe the fuel pump in action.

                July 16, 2016 at 7:59 pm #40336
                frankr
                Participant

                  US MEMBER PAY BY CHECK

                  You say you installed a new in line filter. Does that mean the one in the bottom of the carburetor? Or did you add another one? The ones in the glass bowl are notorious for getting restricted and causing gas starvation. If you added another filter, just remove the one from the glass bowl.

                  BTW, those glass bowls normally run nearly empty. Don’t try to understand it, just believe. The fact that it is full sort of suggests the filter is clogged–OR you are mashing on the primer bulb.

                  July 16, 2016 at 8:02 pm #40337
                  frankr
                  Participant

                    US MEMBER PAY BY CHECK

                    I don’t know much about the mikuni pumps, but normally the hose length from the tank doesn’t matter. Unless you have the tank placed over on the other side of the river.

                    July 16, 2016 at 8:07 pm #40338
                    mnmarty
                    Participant

                      I’ll remove the bowl metal filter. I put another in the gas line for extra protection. I sure hope that’s it. It would be the easiest fix. If that is the problem, what do people do with those filters to get them clean?

                      July 16, 2016 at 8:56 pm #40340
                      frankr
                      Participant

                        US MEMBER PAY BY CHECK

                        Well, you are supposed to throw them away and replace with a new one. But some people claim they get them clean with carb cleaner. Hate to admit it, but I just throw it away and go without one. There is a nice fine filter in the gas tank and another in (most) fuel pumps. Like I said, I don’t know about the mikuni though.

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