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  1. #1
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    HELP! I am stuck at 75.5 mph !!! GROUP K MOTOR

    Ok I have been working on getting this ski running 78mph to 79 to compete with two freinds of mine that run Jacked UP RXP's.
    I have been on the phone with all the gurus and THEY ALL HAVE been VERY helpful. But I am missing something so I will post what I know I have, And maybe the speed demon can be found so I can KILL IT! .

    I have:
    2002 1200 motor now 1390 group k motor.
    hull has 120 hrs on it
    tunnel renforce
    OLD style r&d ride plate modded by me to for top end.
    new wear ring SS
    plugs indexed and j gapped
    D plate.
    Jet works mod with 3/8 hose
    concord 14/20 pitched to 14.5/24
    2002 pump
    VF-3 reeds
    3* keyway
    # 3 cylinder dumping water over.
    pilot 95 mains 120
    1 turn out on lows
    1.5 turns out on highs # 1&2 cly #3 at 1 7/8 (plug looked lean.)
    (I have 115 pilots and 125 mains on the way)
    pump is sealed and shoe is not hanging.
    1200 R&D intake
    2002 tabs (metal) shimmed .034 front two bolts .054 rear bolts
    pro-tec FA's
    Hull sanded.

    I have not filled any holes in shoe or ride plate or tabs. I am not sure I am where I want to be yet.


    Here is the storie:

    lately I thought maybe the impeller I pitched might have been out of wack? 75.5 mph @ 7210 rpms
    So a freind lent me a impeller that he had done by a pro. it is a 14/20
    pitched up to 14.5/21. I tried it this morning. ran 7310 rpms @ 75.3 mph

    Can any one help this. I can send pics of any size or flavor. I need 3 mph.


  2. #2
    mrbtd's Avatar
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    Jul 2005
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    Lindenhurst, Illinois, United States
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    Venturi ?

  3. #3
    flyboy's Avatar
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    Nov 2005
    Location
    Destin, FL
    Posts
    1,585
    I think your prop is wack too.

    you went from a 14.5/24 to a 14.5/21 and gained 100 rpms, but lost only .2 MPH.
    I think you might need to try someone elses big prop.
    also you are running a 1200 grate.
    why are your tabs shimmed like that? is your ski bouncing without shimms?
    do you have the 2 inch spacer installed?

    just a few things I can think of

  4. #4
    ou812's Avatar
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    Jun 2006
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    Quote Originally Posted by great lakes gpr 1200 View Post
    Ok I have been working on getting this ski running 78mph to 79 to compete with two freinds of mine that run Jacked UP RXP's.
    I have been on the phone with all the gurus and THEY ALL HAVE been VERY helpful. But I am missing something so I will post what I know I have, And maybe the speed demon can be found so I can KILL IT! .

    I have:
    2002 1200 motor now 1390 group k motor.
    hull has 120 hrs on it
    tunnel renforce
    OLD style r&d ride plate modded by me to for top end.
    new wear ring SS
    plugs indexed and j gapped
    D plate.
    Jet works mod with 3/8 hose
    concord 14/20 pitched to 14.5/24
    2002 pump
    VF-3 reeds
    3* keyway
    # 3 cylinder dumping water over.
    pilot 95 mains 120
    1 turn out on lows
    1.5 turns out on highs # 1&2 cly #3 at 1 7/8 (plug looked lean.)
    (I have 115 pilots and 125 mains on the way)
    pump is sealed and shoe is not hanging.
    1200 R&D intake
    2002 tabs (metal) shimmed .034 front two bolts .054 rear bolts
    pro-tec FA's
    Hull sanded.

    I have not filled any holes in shoe or ride plate or tabs. I am not sure I am where I want to be yet.


    Here is the storie:

    lately I thought maybe the impeller I pitched might have been out of wack? 75.5 mph @ 7210 rpms
    So a freind lent me a impeller that he had done by a pro. it is a 14/20
    pitched up to 14.5/21. I tried it this morning. ran 7310 rpms @ 75.3 mph

    Can any one help this. I can send pics of any size or flavor. I need 3 mph.
    Looks like you gained 100 rpm & only lost .2 mph. 100 rpm is good for 1.2 mph or so. isn't the target rpm 7200'ish for the 1390? Maybe a 14.5/22 done by a pro will do ya for 2+ mph.

  5. #5
    My son (mohawk man) jeffsntx's Avatar
    Join Date
    Sep 2006
    Location
    Belton TX
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    2,598
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    Quote Originally Posted by great lakes gpr 1200 View Post
    Ok I have been working on getting this ski running 78mph to 79 to compete with two freinds of mine that run Jacked UP RXP's.
    I have been on the phone with all the gurus and THEY ALL HAVE been VERY helpful. But I am missing something so I will post what I know I have, And maybe the speed demon can be found so I can KILL IT! .

    I have:
    2002 1200 motor now 1390 group k motor.
    hull has 120 hrs on it
    tunnel renforce
    OLD style r&d ride plate modded by me to for top end. How much angle?
    new wear ring SS
    plugs indexed and j gapped
    D plate. Which one??
    Jet works mod with 3/8 hose
    concord 14/20 pitched to 14.5/24 You need the 05 and up pump.
    2002 pump You need the 2" spacer
    VF-3 reeds
    3* keyway
    # 3 cylinder dumping water over.
    pilot 95 mains 120 Seems a little low to me
    1 turn out on lows
    1.5 turns out on highs # 1&2 cly #3 at 1 7/8 (plug looked lean.)
    (I have 115 pilots and 125 mains on the way) This may be just a little lean still.
    pump is sealed and shoe is not hanging.
    1200 R&D intake
    2002 tabs (metal) shimmed .034 front two bolts .054 rear bolts Why are the tabs shimmed? Did you have a bounce at high speeds?
    pro-tec FA's
    Hull sanded.

    I have not filled any holes in shoe or ride plate or tabs. I am not sure I am where I want to be yet.


    Here is the storie:

    lately I thought maybe the impeller I pitched might have been out of wack? 75.5 mph @ 7210 rpms
    So a freind lent me a impeller that he had done by a pro. it is a 14/20
    pitched up to 14.5/21. I tried it this morning. ran 7310 rpms @ 75.3 mph

    Can any one help this. I can send pics of any size or flavor. I need 3 mph.
    I am by NO means a GURU but this is just what jumps out at me.

  6. #6
    JetSkiDaddy's Avatar
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    May 2005
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    Houston, TX
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    I would start with new style pump and Dynafly

  7. #7
    flyboy's Avatar
    Join Date
    Nov 2005
    Location
    Destin, FL
    Posts
    1,585
    oh yeah, i forgot, Open up your D plate a bit

  8. #8
    MPower's Avatar
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    May 2005
    Location
    Raleigh, NC
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    Quote Originally Posted by flyboy View Post
    oh yeah, i forgot, Open up your D plate a bit

    +1

  9. #9
    GPRPITMAN's Avatar
    Join Date
    Feb 2006
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    capecoral fla
    Posts
    880
    Great lakes call me if you like I can give you my old set up on my group k doing over 81 239-340-1372
    Forrest

  10. #10
    Duke's Avatar
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    Florida
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    If Forrest offered you better take it and call him.

    The jetting looks way off to me. I run 125m in my unported 1200, I would thing 140 or at least 135 to start off with. Did you talk to Harry at Group-K about jetting? You would also benefit from the new style pump. The shoe could be a culprit as well, what are the measurements stepping up from the hull. Also what kind of angle do you have on your modified plate?

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