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  1. #1

    1999 Gp1200 Slow Holeshot. Help!!

    Hey all,

    So yesterday having fixed most of the bugs from the recent shakedown/break-in on my 1999 GP1200x restoration project, it actually runs great. The issue I think I'm having right now is that it doesn't have that good of a holeshot. But once it hooks up it GOES. I have a feeling that it is cavitating on me.

    I am seeing 7000-7100rpm on the stock gauge and runs 59-60mph on the Dream-O-meter.

    I am not sure if the impeller is stock or aftermarket. I'm planning on taking the driveshaft/impeller assembly off tonight to check. I'm also bogging a tiny bit at about ~1-20% throttle, but I think that's because I probably have the carb setting a bit rich.

    What would be a good fix for cavitation? I'm planning on getting a Solas XO 14.5-17.5 OR better yet a 14.5-18 impeller.

    Specs:

    1999 GP1200 65U
    running 40:1 premix
    .50mm Overbore
    choke plate removed
    open carbs - still have to get aftermarket flame arrestors
    135 main jet
    100 pilot jet
    ~55psi popoff


  2. #2
    Little Update: I could not for the life of me remove the the stator, impeller, and d/shaft straight out the back. I already removed the ride plate to give me some more room to pry on the tabs but even after soaking it with penetrating oil and hammering the shit out of it using a dead blow, the assembly still wont budge. And I have checked and verified that all the bolts are out. It should only be the 4 long bolts that's holding that in correct?

    Also, when removing one of the 4 long bolts, 1 of them snapped on the threaded area so now I need to really get in there so I could remove the bolt and put a new one on.

    Any help, advice?
    Last edited by bford; 06-29-2015 at 10:22 PM.

  3. #3
    Well had to remove the whole pump housing assembly underneath to separate the driveshaft/impeller section of it.

    My main issue that I need any of you all's advice is that, I feel that my ski is cavitating from the hole. It's pretty sluggish when trying to get up to plane from a dig. I assumed that these gp1200s would literally JUMP out from the hole and fast. If I go and modulate the throttle I get to plane faster and once I get to plane i still have the speed and power. I see 60mph @ 7000rpm on the stock speedo (i know the general consensus with the speedo is not accurate)

    I'm waiting for a used solas XO 14.5-17.5 to come in the mail and see if I get less cavitation. I had to remove the whole pump housing assembly because when I tried to remove the 4 long bolts, the impeller and drive shaft didn't budge any...even with prying. So anyway while I have everything out, what other mods should I do there besides from the impeller?

    I have read about sealing something but I'm not too sure how to do that.

    Any input/help please. Thanks.

  4. #4
    Budman's Avatar
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    Jul 2008
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    Montana
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    The gap between the impeller and wear ring is vital for a good hookup but I can't seem to find the gap measurement. my factory impellor had issues that turned out to be a small piece broken off. Cavitation usually comes with a vibration and a noticeable jump in RPMs. lots of other things can effect hole shot. On mine "The Judge" told me to lower the pop off to 30 and wow did that make a difference.

  5. #5
    Hey Budman,

    I have also read about the gap between the wear ring and impeller but I also could not find the measurement/spec. I tried looking at the manual but I couldn't find it there.

    I don't think the popoff should affect cavitation directly though since that's on the carb side.

    I'll go grab some pics of what I have and post it so you guys could tell me if I got something wrong or my parts are fine.

  6. #6
    Yamaha artisan Cutlass's Avatar
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    Oct 2010
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    Madison, WI, USA
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    the impeller needs to fit very tightly in the wear ring but without touching it. The clearance should be less than .024" with an ideal range of .010" to .015". A feeler gauge works best but a normal business card is about .012" thick and can be used to get an idea.

  7. #7
    Well, I found one of the problems. Just checked the clearance between impeller and impeller wear ring housing and I could slip a 0.025" feeler gauge. Gonna get back with a picture of that intake duct housing piece for you guys to check if I have any issues before water passes the impeller.

  8. #8
    butterbean_29512's Avatar
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    Sep 2013
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    Spec is .010-.020, service limit .024. My clearance on my 2000 gp1200r is about the same as yours, and it does the exact same as yours. Cavitation out of the hole, but once it books up it goes hard. New pump parts on the way.

  9. #9
    Prism's Avatar
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    This year and model ski should have awesome holeshot. Zero or nearly zero cavitation.

  10. #10
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    Here's the pictures of the pump tunnel housing and the part in question. Would this also cause my cavitation? I don't know how that damage could happen but it has.

    Also should I sand that down so everything is nice and flat/even and smooth?

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