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  1. #1

    ** NO pop-off pressure on my 1993 Waverunner **

    Hello forum,


    we a yamaha waverunner 700 WBX from 1993.
    Carburetor (Mikuni 44mm) has been rebuilt now twice but still is giving us problems.


    Hard start (we now switched to primer which helped a bit), and after a 10min run or so it does not start at all anymore.
    When I am back at home from the boat launch it usually starts again.


    Sounds all like a possible needle and seat problem.


    So I got a new set of needle and seat from SBT, this Yamaha has a 1.5 seat.
    I also bought a pop off pressure pump to test the pop up pressure and another rebuilt kit to have it all "perfect".


    Unfortunately after many many tries ... there is no pop up at all, the N/S is not holding any pressure.
    Its hard to say but the gauge never goes over 2-3 psi, so basically nothing.

    Double and triple inspected the N/S, switched out spring and arm.


    If someone has an idea what to check or what I might be doing wrong ... very much appreciated.


    Sorry ... yes I used some WD40 to have the needle wet.

    Thanks
    .axel
    Last edited by borcherta; 06-19-2020 at 10:32 AM.

  2. #2
    It's got to be wet, did you use a little WD40 on the needle and seats when testing? Also you have to block off the other nozzle.

  3. #3
    yes, I did spray some WD40, I followed the detailed pop-off video from SBT ... sorry I forgot to mentioned it, changed it in my original post.

  4. #4
    Hello and sorry forum for bumping this up again. I made 2 videos to hopefully now explain myself better ...




    Video 1: trying to pump, its not holding pressure, like *nada*






    Video 2: now using the shop hose instead, the mechanism spring/needle seems to be working








    Is my return and pulse not perfectly blocked off?


    I am using a sbt pump.
    If I put my finger on the outleet of the pump and start pumping, the gauge shows pressure. So the little pump seems to be ok.


    What am I doing wrong (?)
    Thanks!

  5. #5
    After playing more for a while, it was the gasket of the seat.
    Its old, bad and brital ...


  6. #6
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    find yourself a new rebuilder, whoever did that for you was the worst kind of hack.

    checking for leaks around the seat is SOP by the way.

    crud accumulates there too so always remove them for cleaning and replace the o-rings. clean the seat area really well with some carb cleaner and my favorite go to, gun cleaning patches. lube it really well and press it straight in

    my other guess would have been your gauge was leaking. that style doesn't last too long ( ask me how I know) the style that looks like a bike pump is much better and can move enough air to pressurize a fuel tank, which comes in pretty handy and they only run $20-$30 more

  7. #7
    Quote Originally Posted by nmpeter View Post
    my other guess would have been your gauge was leaking. that style doesn't last too long ( ask me how I know)
    Thanks for your input and helping out the amateurs
    I wish I had a "jetski tub" like the one you have on your website, would have saved me lots of unsuccessful trips to the launch.

    I have new piston/cylinder from SBT and the carb rebulit on my 1993 Waverunner.

    SBT calls for 25-35 psi pop off while all being stock, this does mean the engine needs to produce around 30 psi suction to make the needle open up and let the fuel flow, correct?
    We are doing the pop off test with the hand pump from the fuel side, but the "fuel pressure" is not what opens the needle when riding on the water, correct?

    Thanks!

  8. #8
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    Correct, the carb diaphragm is what opens the needle to allow fuel flow

    as the fuel is sucked into the engine thru the jets the atmospheric pressure on the other side of the diaphragm presses down and uses the leverage of the “float arm” to lift the needle. You’ll notice a small vent hole in the carb cover for this purpose. The float arm adjustment is critical as is using the correct spring

    Having the test tank was vital to the success of my business reducing my comeback rate to near zero as I could always assure strong running engines after carb work and easy restarts

    My first year I realized how much time I was killing dragging skis up to the lake for a performance test

    Bought the tank soon after the end of season#1 got far more work billed at the end of season #2

    In hindsight I should have bought the Jetski dyno for a grand or two more since the newest skis now exceed the tank capacity

    I’ll be selling the tank next season since I’m no longer working on two strokes in Prep for my retirement (just turned 62)

    I price in 90 minutes of lake test time on all my 4 stroke driveline and engine work these days

    Still don’t like dealing with lake testing...kinda exhausting if I have to make three trips a day

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