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  1. #1
    robisthemantis's Avatar
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    HELP!! Stuck at 71mph 🤕

    Hi guys

    Does anyone have any suggestions on things to try to get me going better, Iíve heard these skis can get to mid 70ís without touching the motor.

    The ski is a 2006 GP1300r and I canít get past 71mph, I donít want to open the motor up for reliability

    heres my list of mods, any help is much appreciated

    SKI HULL SETTINGS


    Stock tabs spaced .067Ē
    1 degree pump wedge
    Protec extended nozzle
    PPK
    Stepped stock sponsons
    Riva 1200 intake grate, I ride in the ocean so the 800 grate doesnít suit.
    1200R R&D ride plate set at .950Ē and flush between front of plate and shoe
    Trim and steering centred
    Jet works valve
    Blue printed HO pump with out of the box solas dynafly 14/20
    Free flow exhaust (it stays I like the noise)
    R&D power plenum
    Riva fuel controller 2-4-1-6
    Cowling air intake cut to match both sides


    18 degree weather with slight chop
    71 Mph average
    7150 Rpm

  2. #2
    Mike's GPR's Avatar
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    Quote Originally Posted by robisthemantis View Post
    Hi guys

    Does anyone have any suggestions on things to try to get me going better, Iíve heard these skis can get to mid 70ís without touching the motor.

    The ski is a 2006 GP1300r and I canít get past 71mph, I donít want to open the motor up for reliability

    heres my list of mods, any help is much appreciated

    SKI HULL SETTINGS


    Stock tabs spaced .067Ē
    1 degree pump wedge
    Protec extended nozzle
    PPK
    Stepped stock sponsons
    Riva 1200 intake grate, I ride in the ocean so the 800 grate doesnít suit.
    1200R R&D ride plate set at .950Ē and flush between front of plate and shoe
    Trim and steering centred
    Jet works valve
    Blue printed HO pump with out of the box solas dynafly 14/20
    Free flow exhaust (it stays I like the noise)
    R&D power plenum
    Riva fuel controller 2-4-1-6
    Cowling air intake cut to match both sides


    18 degree weather with slight chop
    71 Mph average
    7150 Rpm
    Itís been a little while since I set up a fast GPR, but here are my thoughts. 71 is damn good on a ski the motor has not been touched.

    You really need to think about that pump wedge, the .950Ē goes out the window and you need to test, test, test

    Also is your ride plate stock or modified?

    Is your pump sealed?

    Is your pump tunnel reinforced?

    Thoughts on your wrench skills for advancing your timing, reeds, etc

    Stock GPRís donít go mid 70ís without engine mods. Unless your dead on with every trick out there.

    EFI controller is not needed, if you want to use it- add compression at a min.

    .067 trim tab washers seam a little thick, thought it was closer to .045

    Where are your RPMís? Need accurate rpms.

    Free flow, costing you 50rpms

    Extended nozzle is costing you speed

    And the tricks go on and on and on.

    To get a GPR to run mid 70ís you need a lot and good set up. To get to 80 you need a real lot including porting and or big bore with everything set up perfect


  3. #3
    robisthemantis's Avatar
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    Feb 2014
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    Hi Mike

    Thanks for taking the time to reply!

    I will get that pump wedge off and play with the plate angle some more see if I can find a gain, I’m not sure how guys are getting more angle than me as I had to remove the pump bolt washers and grind the top of the plate to get it to clear the pump.

    Since I live in New Zealand I don’t have access to guys that know what they’re doing with ride plates so I’ve done the work myself trueing the ride surface and grinding the mounts to get more angle.

    Yes the pump, shoe and transom plate is sealed, gay spray delete and d-plate installed

    No holes filled yet.

    Yes pump tunnel reinforced.

    More than happy to do anything as I’m a qualified mechanic but I’ve stayed away from engine mods on this ski mainly because I ride ocean and had a 03 with compression and timing advance and lost a motor when the fuel controller stopped working- not what you want out at sea.

    I use the fuel controller to ritchen up a little since I hear these motors run a little lean in the midrange, I’m only at #2 on the low end and I’m adding 1/4 an ounce of oil to every gallon of fuel - I figure the slight bit of extra fuel and oil will only help longevity.

    Great I will test with some .045” washers and see if I can gain some!

    Might be time to upgrade my cheap Chinese tacho haha.

    Will try the stock plastic nozzle next time out too!

    Thanks again mike you’ve given me something to work on and glad to hear I’m close to where I should be

  4. #4

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    This brings me way back....I use to have a new '06 gpr.
    Sounds like you have a very good setup right now to be running 71 on a 1200 grate. 800 grate and put the sound suppression back in and it would be 73+ I'm sure.
    At one time I had my ride plate at over 1" angle. Its possible grinding the plate and pump/nozzle by hand. There's probably only a little speed from .950 to around 1.10" but at the low 70mph range I think it can use that much angle....if it does start to bounce you can tame it by shimming the trim tabs. You also don't have to shim the whole tab equally, you can shim the rear more than the front.

    I ran without the air box on mine when it still had efi and used velocity stacks on the throttle bodies that were meant for a 4 stroke ski at the time.

    If the Vforce reeds are still available, that would give you 120 rpm gain and you could then easily pitch the prop up giving you even more mph.

    We always filled the 4 pump shoe bolt holes....I would put some tape over the bolt head first before filling them.


  5. #5
    robisthemantis's Avatar
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    Thanks Ronn

    I see you’ve owned some fast GPR’s in your time, for me the new skis are out of my price range right now and I like how the little GPRS look and go for the $$ invested, I have another hull kicking around I’ll drop a 1800 s/c motor in once we build our house and I have some more tin.

    As you suggest I’ll get the grinder back out and see if I can eek a little more angle out of that plate, and I’ll fill the holes but leave the plate holes so I can still tweak it.

    I’d love to do the reeds but woh they cost a lot by the time you get them down here, maybe next year.

    seems like going where I should be for what’s been done by the sounds of it tho at least.

  6. #6

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    Your ski is running well for those mods. The Gpr is a good efficient hull for top speed...hard to beat for the money. I'd like to get another one myself. I've been away from ski's for several years now but recently bought a gp1800 to mod. Keep us posted on the progress of yours.


  7. #7
    robisthemantis's Avatar
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    Amazing how popular these skis are or were, they sure do seem to go well for the little power they have.

    Thanks again Ronn, will do.

  8. #8

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    Check out the speed database in the sticky section.... lots of tried and true tuning.

    Also, have you milled the head,? .020 can bump your compression up and wake up the ski.

    We plan on doing head work on our 1200R this winter.
    Last edited by K447; 09-26-2020 at 08:56 AM.


  9. #9
    robisthemantis's Avatar
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    Thanks Jonesy,

    I have seen that speed database - some crazy speeds in there that’s for sure!

    I have read al lot of what’s been written, unfortunately I think most have moved on from modifying these skis and are onto the new supercharged machines so I’m hoping someone will share some of the knowledge that some of the real serious guys had about setting up the gprs years ago that they kept secret to win races or to profit from passing on.

    I’m trying to stay away from modifying the motor for reliability, iv had one let go on me in my 2003 Gpr years ago and thy cost a fortune to repair just on parts when they go so I figure with this one I’ll just do the hull and leave the motor.

    Cheers for the reply

  10. #10

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    We are in the same boat.... sorta. We’re working on a 01 GP1200R with unknown hours due to a bad dash. The best was had on the speedo was 67 before an oil line issue. Then we went premix and now have a high idle issue... we’ve been down since June. I am finally working on the carbs and also acquired a pressure kit, so we will see where this takes us.

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