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DT 55 Fuel Pump or Air Leak or Both

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  • DT 55 Fuel Pump or Air Leak or Both

    Hi; I have a 1987 DT 55 2 stroke triple, old but reliable. Starts fairly well, idles well enough for the year, runs okay at wide open throttle, issue appears at mid throttle say 1/2 -3/4 open, motor surges (speeds up then slows down) it feels like either air or fuel starvation. pretty cyclic in nature. In the garbage can with the muff on doesn't due it with the fast idle seems to be when under load.

    I have tried to adjust the carb pilot air scres but doesn't smooth it out, might lessen the effect but still there. I have replaced the primer bulb, no viable cracks or kinks in the air lines, vents on tanks are open (been caught on that recently) I still have to check the pickup line inside the tank and needle valve on tank for leaks.

    Question; Can this be an indicaiton of the fuel pump diaphram wearing out? I have also replaced the fuel filter.

  • #2
    Re: DT 55 Fuel Pump or Air Leak or Both

    Time for a proper carb clean ....
    __________________________
    ... THE MAXIMUM HORSEPOWER IS NEVER ENOUGH ...

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    • #3
      Re: DT 55 Fuel Pump or Air Leak or Both

      Originally posted by deejaycee_2000 View Post
      Time for a proper carb clean ....
      Carbs have been completely rebuilt (thanks to Ethanol) only run Octane 91 or 94 with Marine Stabol in there.

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      • #4
        Re: DT 55 Fuel Pump or Air Leak or Both

        In that case I would replace the fuel pump diaphram ....
        __________________________
        ... THE MAXIMUM HORSEPOWER IS NEVER ENOUGH ...

        Comment


        • #5
          Re: DT 55 Fuel Pump or Air Leak or Both

          http://forums.iboats.com/engine-freq...em-283363.html
          this shows how to test fuel system, and using the clear tubing for testing will show if it is sucking air.
          I have seen cracked pick up tubes before in the plastic fuel tanks, but any connection on suction side of pump can be a source for air

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          • #6
            Re: DT 55 Fuel Pump or Air Leak or Both

            Originally posted by 99yam40 View Post
            http://forums.iboats.com/engine-freq...em-283363.html
            this shows how to test fuel system, and using the clear tubing for testing will show if it is sucking air.
            I have seen cracked pick up tubes before in the plastic fuel tanks, but any connection on suction side of pump can be a source for air
            Thanks all, good sage advice, good forum!

            I was planning on rebuilding the fuel pump since it is pretty inexpensive for the parts and simple to do, plus I have no idea when service was last done on this part if ever.

            I will definitely be walking the system for air leaks (I'll start with the clear tube method first) , I suspect one of my tanks when <1/2 full as the major issue, however running from the other tank I never completely got rid of the issue hence the fuel pump plus sometimes it is a little hard to start (starts but then dies off after a couple of seconds) re-prime required to catch.

            Engine is definitely wanting either more air or gas or combo of both, but pretty solid overall,

            It gets used very hard with all the teenage kids and towing etc.

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            • #7
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              Well it turned out to be the fuel pump. Purchased the repair kit a couple of diaphrams and a spring for ~ $20.00, a 10 minute repair....runs great now, full throttle response. I also propped it down a pitch since we tow with it....as a bonus starts easier as well.

              I guess the 27 year old rubber diaphrams became a little stiff and inefficient overtime.



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