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  1. #1
    Petron's Avatar
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    Mikuni pop-off pressure

    Hopefully someone can explain this one.

    I'm rebuilding my Mikuni BN-401 (SB) carbs (1996 SeaDoo GSX). The manual calls for pop-off pressure ranging between 23-43 PSI.

    Good news is my pressure is reading at 30 PSI.

    Bad news is once I install my new regulator diaphragm & regulator chamber cover I decided to check pop-off pressure again (before completing rebuild) and pressure reads at 18 PSI +/-.

    I have new needle & seat (1.5 size), dull silver spring, along with rebuild kit that I've used.

    Any explanations? Thanks


  2. #2
    Pro-pulsion's Avatar
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    Possibly the needle valve lift tab is set too high or too low. If the tab is too high, the spring will be less compressed making a lower required pop-off pressure, if the tab is sitting low then you have too much spring tension and the diaphragm will have to travel further to open the needle valve making a higher required pressure.

    I think the way to check it is with a ruler using the end to bridge across the the carb body over the lift tab. Don't quote me on this but I believe that the tab should be flush with the carb body and as close to touching the ruler as possible without there being any tension against it.

  3. #3
    96XPSS's Avatar
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    Make sure the needles are wet when you check pop-off.

  4. #4
    Petron's Avatar
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    I think I may have discovered the issue. I purchased a new needle/ seat package from SBT (1.5mm) & after trying many times to get consistent pressure readings I resorted back to original needle/ seat (new o'ring).

    Now I'm getting consistent 32 PSI.

    I noticed the base of the new seat (from SBT PACK) was actually slightly different to the original mikuni one (I'll try post pics.)- go figure.

    Now should I settle for a seadoo recommended 30psi +- 10 or mikuni recommended 43psi. ?

    What are you guys going for? Has it been working?

  5. #5
    Moderator beerdart's Avatar
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    When replacing carb parts always use genuine parts.. Its not worth the hassle to save some$$$

  6. #6
    96XPSS's Avatar
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    Quote Originally Posted by beerdart View Post
    When replacing carb parts always use genuine parts.. Its not worth the hassle to save some$$$
    +1

  7. #7
    96XPSS's Avatar
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    Quote Originally Posted by Petron View Post
    I think I may have discovered the issue. I purchased a new needle/ seat package from SBT (1.5mm) & after trying many times to get consistent pressure readings I resorted back to original needle/ seat (new o'ring).

    Now I'm getting consistent 32 PSI.

    I noticed the base of the new seat (from SBT PACK) was actually slightly different to the original mikuni one (I'll try post pics.)- go figure.

    Now should I settle for a seadoo recommended 30psi +- 10 or mikuni recommended 43psi. ?

    What are you guys going for? Has it been working?
    Leave them at what you currently have this is a little on the low side which opens to the main jet quicker, giving you better throttle response. To be honest, none of us ever tweaked pop-off on a stock ski. Put some Fly's and rejet and you'll save almost 30% in fuel consumption.

  8. #8
    Petron's Avatar
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    Sometimes you get so involved you start raking your brain. Thats my outcome also, just let it be. Thanks guys

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