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  1. #1

    OK 49.7 MPH at 6950 RPM whats wrong?

    I posted this problem before but didn't actually GPS the speed. THe factory speed was actually right on. Not even doing 50MPH.

    Engine runs strong sounds good. Its WOT RPM is between 6940-6960 on flat water. This is only after I shimmed the R&D rideplate so it would stop porpoising. Shimmed it just under 0.5 inches on the rear.

    The ski porpoised like crazy before I shimmed the plate and its still a little squirly in chop but OK on flat water.

    The ski has:
    R&D rideplate
    R&D intake grate
    K&N flame arrestors

    Everything else appears stock I'm not sure what impeller is on it (I'm assuming stock but maybe not). Any ideas? Oh and it sounds like a beast much deeper than my GPR but the exahust looks stock.

    Any ideas? I want to put triple pipes on but I need to get the ski running right stock first.


  2. #2
    Check for exhaust leak, just had this problem on my GPR where i cracked the exhaust manifold.

  3. #3
    Quote Originally Posted by 00gprNC View Post
    Check for exhaust leak, just had this problem on my GPR where i cracked the exhaust manifold.
    Aren't my RPMs where they are supposed to be though? If I had an exhaust leak wouldn't I figure I would lose RPM right? What RPM does a stock GP1200 turn normally? If its turning close to the right RPM then I am thinkink its got to be a hull or pump problem.

  4. #4
    Mpeavler's Avatar
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    prop clearance excessive?

    RPM's should be higher though...over 7k

    M

  5. #5
    Quote Originally Posted by 00gprNC View Post
    Check for exhaust leak, just had this problem on my GPR where i cracked the exhaust manifold.
    Quote Originally Posted by Mpeavler View Post
    prop clearance excessive?

    RPM's should be higher though...over 7k

    M
    Really I thought stock RPM was right at 7K. Which is pretty much were I am at. What exactly is stock WOT RPM???

  6. #6
    WATER WOODY's Avatar
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    Your running FA's without rejetting! gpr?

  7. #7
    Mpeavler's Avatar
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    Kev

    don't these run around 7100 ish?

    m

  8. #8
    Old Ski Insanity w/rpm500's Avatar
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    yes about 7100 would be ideal for the GP 1200.. as MP says what does your impeller look like.. clearance at the ring may be excessive(bypassing thrust .. but IMT it then should spin up higher than the rpms your stating) or is it possible you have a ding or two in the impeller or the hub stater?... a gp760 twin in this same 'limited mod' set up ,will hit the 50 mph mark pretty consistantly.. the f/a's IMT, would just need a bit more open on the needles, not so much as needing a full jet change...unless hes got more than that going on in the engine mods. dept..

    where are you located ? heat , humidity and elevation play a big part in how you ski performs...MP can definatly tell you how much heat and humidity of the orlando area can kill a skis performance and woody can inform you on the elevation angle.. (i'm assuming your here in central fla 'cause of your ucf name abreviation)

  9. #9
    quadzilla's Avatar
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    Lightbulb ???

    Hey there UCF...

    You are correct in thinking your RPM's are where they need to be..

    With a stock CDi unit the the factory rev limit is right about 7050 rpm

    So with everything being stock..??
    The F/A's don't really change anything since the GP runs a virtually open airbox anyway..!!
    (maybe needing an eighth to a quarter out on the highs..?? Osidebill is the guy to ask about this..!! )

    Then if its not cavitating like crazy out the hole or anywhere else..

    I'd have a guess at your prop being totally screwed out of shape (pitch)..
    Likely have at least one of the blades all bend to hell and beyond..!

    You certainly appear to be giving away about 10mph somehow..???

    I'd definitely be either pulling the grate off and looking into the front of the prop..
    Better still, Would be to pull the pump out and give it the once over..

    Gerry

  10. #10
    This is on the older GP1200 in case anyone was confused.
    I am actually in Fort Walton Beach (NW Florida). Its hot and humid but I don't think I should lose 10MPH.
    I think my RPMS are pretty close to correct. Its an SBT block so I figured a minor power loss anyway but even if I got it up to 7100 I don't see that giving me 10MPH. I played with the carbs for a while trying to get more RPM out of it and it pretty much stayed the same and maxed out at about 6960. So I put it back too just a little fatter than OEM spec and called it good.
    The engine I think is running where it should be I really think its a pump or hull issue.

    One thought that I had was that the prop pitch is too low and I am hitting the rev limit. But it doesn't feel like I am hitting a rev limit unless its a really soft limiter.

    I have not pulled the pump. I am not too familiar with what I am looking for on it obviously if I see dings its bad. It doesn't seem to be cavitating really bad. I really don't know what the deal is. I'll pull the pump out this weekend as see if there is anyting obviously wrong.
    Any advice as to what to look for on the pump and grate?

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