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  1. #1
    qbzonk's Avatar
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    rebuilding gp800 carbs, got questions.....

    When rebuilding my carbs I noticed there were two different types of springs for the needle and seat. Which ones am I supposed to use? The old ones were smaller than either of the supplied two springs. Will it make a difference which ones I use?

    Also any recommended setting for the high and low speed screw seetings? Right now they are all out 1 1/4 turns out from full (screwed in).

    Thanks for the help.


  2. #2
    cfgp927's Avatar
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    carb rebuild

    The different size springs along with n/s size will definitely make a difference. Both the springs and n/s set pop-off. I'll have to dig out the manual and see where the settings should be for stock. Do you have any mods? F/A, head, exhaust? This will make a difference as to which springs and n/s.
    Mike

  3. #3
    qbzonk's Avatar
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    Quote Originally Posted by cfgp927 View Post
    The different size springs along with n/s size will definitely make a difference. Both the springs and n/s set pop-off. I'll have to dig out the manual and see where the settings should be for stock. Do you have any mods? F/A, head, exhaust? This will make a difference as to which springs and n/s.
    Mike
    I bought the ski used last year. It was set-up for buoey(sp?) racing. I can attach photos of my carbs when I get home later.

    From what I can see I have F/As. Seems to me the accelerator pump on the carbs was removed. The spacer plate they mount to seems aftermarket and the only exhaust mod I can see is an aftermarket waterbox (very loud). Not sure of any internal mods. I can see the reeds, but have yet to remove them and I have no idea what's going on in the cylinders.

    I can also get you my jetting when I get home and open the carbs again.

    the "gram" notation for the springs is the compression resistance not the actual weight of the spring correct?

  4. #4
    qbzonk's Avatar
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    OK, I got home and wifey threw out the garage trash, so here's what I found.

    The pic below has 6 springs in it. I do believe the one on the LEFT is the original. I do know the one on the RIGHT is the new one I put in (largest in the rebuild kit). #2 & #3 are the smaller ones from the rebuild kit. Not sure what the other is, but it was with my spare carb parts.

    From what I could see the main jet is a 130 and the smaller jet is a 120.

    Thanks for the help.
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  5. #5
    oldmanraider's Avatar
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    Here's the Mikuni Pop Off Chart this will shows the difference the spring size will make. If your skis throttle response was good from idle to mid throttle it's probable a good idea to keep the same spring size.

    I like to set my pop off pressure the same on each carb. to do this you will need a pop off tester, I think they cost about 50 bucks.
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  6. #6
    qbzonk's Avatar
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    It tended to bog when you slammed it WOT from idle for split second when I had her running.

    What exactly does this system do? I'm guessing under a predetermined pressure the diaphragm pushes downward and activates the arm and opens the needle from the seat???

    Any downside to having too soft a spring as opposed to too hard? Lean vs rich?

  7. #7
    oldmanraider's Avatar
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    Here's a link to the Mikuni Manual for the SBN Carbs it gives alot of good info.

    http://www.mikuni.com/pdf/sbn_manual.pdf

    If he springs are to small or the pop off pressure is to low fuel will dribble past the needle and seat and cause the engine to load up at idle. If the pop off is to high the throttle response can be slow to respond coming of idle. Most skis from the factory are set with a higher pop off pressure most of the time above 50 psi. When after market flame arrestors are used there will be less vacuum or signal through the carbs and that is one of the reasons to lower the pop off pressure.

    I'm sure there are people here that can answer this better than me, but this should put you in the right direction. For me I try to read as much as I can but still do alot of trail and error.

  8. #8
    qbzonk's Avatar
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    Cool, I know i've seen directions for a home made pop-off tester on here somewhere.

    Any tips for my high and low speed adjusters?

  9. #9
    Duke's Avatar
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    Never heard of anyone using two different springs. If the ski was
    coughing when you snapped it chances are the popoff is to high
    for the mods it has. I would try the 80 gram springs first, they are
    dark green springs that mikuni refers to as black. I have some if
    Orlando Yamaha doesn't.

  10. #10
    qbzonk's Avatar
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    that's great, but I already put the smaller ones back in the carbs. I was going to check the pop-off pressure later.

    Any suggestions based on my jetting for the low and high speed mixture screws?

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