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  1. #1
    FLjoyrider's Avatar
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    Pop off not popping

    Just got a rebuild kit for my '98 domestic 700. Put new diaphrams in the feul pump, carbs got all new gaskets and diaphrams. Installed needles and new springs then tested the pop off pressure. One carb was great popping at 18PSI (per clymer manual) every time. Got to the other carb (feul pump / PTO carb) and seems to just open at 18PSI and a little more at 20PSI but not really popping open like the other carb. What do you guys think, should I replace the seat? Tried different springs and the same thing just at different pressures (43PSI with the big springs and didnt really pop just seemed to open sortof quick but not really then opened more at 45 PSI). Should I run it or see about lapping the seats with valve compound?? is that even an option? anyway let me know what you guys think.


  2. #2
    FLjoyrider's Avatar
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    Well decided to run it, one more question for you guys tho. Manual says 18-20PSI, but papers that came with carbs say 50PSI.. went with the 18-20 but whats up with the paperwork from SBT saying ot set it at 50??

  3. #3
    ph2ocraft's Avatar
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    Call them and ask why, it makes no sense to me. I know I'd be leaving mine as per Polaris and Mikuni unless somebody has an awesome valid reason I don't know about.
    If their "tech guy" decided to change it I'd want to know it's not by the same "tech guy" that says the SBT engine is not running hot until the paint is discoloring at the cylinders.

  4. #4
    PolarisNut's Avatar
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    Quote Originally Posted by FLjoyrider View Post
    Well decided to run it, one more question for you guys tho. Manual says 18-20PSI, but papers that came with carbs say 50PSI.. went with the 18-20 but whats up with the paperwork from SBT saying ot set it at 50??
    Sounds like a misprint there...the Keihin carbs dont have popoff that high. Sounds like the needle may be binding a bit in the seat. I'd pull it all back apart and have a look.

  5. #5
    FLjoyrider's Avatar
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    I've pulled it apart and put it back together more than a dozen times. I;'ve looked at the seat and can't see anything out of the ordinary, I've looked at the needles (tried new ones and old ones) and nothing really seems to be out of place. One thing I noticed is that it seems to pop the first try after I put it back together.. then after the first try is when it seems to just open rather than pop open. It seals fine below 18psi and the diaphram is what opens it so I don't think it will be a problem? correct me if I'm wrong.

  6. #6
    cheatin' piston popper addicted's Avatar
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    are you keeping the needle wet with wd 40 while checking the popoff?

  7. #7
    FLjoyrider's Avatar
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    yeah, thats how I know its not popping. I spray WD40 in there and then instead of it being blown out as soon as the needle opens, it rapidly bubbles out (@18psi) then finally pops out (@20psi), but I have to add a lot of air to get it to 20 psi.

  8. #8
    PolarisNut's Avatar
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    It's got to be a bad needle, seat, or the arm is binding...thats all it could be.

  9. #9
    cheatin' piston popper addicted's Avatar
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    pull the needle out and look for a ring in the rubber tip from contact with the seat. If it's bad enough, you will get exactly those symptoms. Only fix is a new N&S assembley.

    What sucks is that the rubber cap thingy that they ship them in actually wears them out before they are installed if the person packing them pushes it in too far.

    Also, make sure that the o ring around the seat isn't your culprit. Put on your safety glasses and watch for the bubbles.
    Last edited by addicted; 09-13-2007 at 08:46 AM.

  10. #10
    FLjoyrider's Avatar
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    The needles are new, and the ring on the rubber seat is the first thing I looked for (perfectly smooth). I also checked those O rings on the other side of the seat, which were also part of the carb kit. Changed them back out with the old ones, tried spinning them around to see if that helped.. if it did it wasn't much. I'll take another look at it tonight if I have time, but I spent two hours on it the other night and the only thing I can really think of that could still be wrong is the seat itself. Since the carb kit didn't come with the seat it might be what I need. Thanks for your help!

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