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  1. #1
    philip_gpr's Avatar
    Join Date
    Dec 2005

    My Blue Ski - step by step instructions

    My blue ski, a not so stock anymore, 2000 GP1200R.

    78+ mph spinning a Solas Dynafly 14/20 pitched at 15/25 7140 rpm.

    Over the past couple years I have had a lot of help from other forum members. I used all of this input when putting together this ski - as always - thanks guys.

    The motor

    Installed a complete OEM GP1300R top end. (cylinders, pistons, PVs and head)

    These cylinders were not ported.

    Installed a Riva 3 piece cast performance head that was machined to further raise compression.

    Compression is now 170 lbs, squish is .045 in. I am only using 1 layer of a GP1300R head gasket.

    Previously I used 2 layers of the gasket. My compression was 160 lbs and the squish was at .050 in. My top speed and rpm numbers did not increase when I raised the compression to 170 lbs.

    With 1200 cylinders (regardless of the CC) you want to use a 1200 head gasket. Likewise with 1300 cylinders you want to use a 1300 head gasket. In 2005 Yamaha used larger holes in the cylinder head gasket for cylinder #3 which will improve cooling due to increased water flow.

    Power Valves

    OEM power valves with the R&D replacement PV arms were installed. I also use the RPM couplers version 1 to remove the slop you get with the crappy OEM couplers.

    Adjusting the Power Valves

    You can gain some additional RPM by adjusting the power valves. The valves open too much at WOT and this causes a loss in RPM. Here is the procedure to adjust the valves. (thanks to Duke for helping me with this)

    Don't bother attempting this if you are not using either the waveeater couplers pr RPM couplers.

    1) Disconnect the electrical connector to the servo motor

    2) Slide the protective rubber cover back so you can see the wheel where the cables connect to the servo motor.

    3) Remove both PV cables, in the middle of the cables are adjustable turnbuckles covered by a rubber cover - cut off the rubber cover and then completely open up the turnbuckles and clean up the threads using a wire brush - you want them so you will be able to turn them freely by hand on the water.

    4) Reinstall the cables.

    5) Rotate the wheel so the PVs are all the way open. The electrical connector is still disconnected so the PVs will stay in whatever position you set them in.

    6) Go for a ride, record your RPM at WOT.

    7) Continue doing speed runs, after each run close the valves a bit, record you RPMs. Find the sweet spot that gives you your maximum RPM.

    Connect up the electrical connector. Using the adjustable turnbuckles adjust the cables so the valves do not open fully at WOT. Using the adjustable turnbuckles you are trying to get the valves positioned at WOT to be the sweet spot you found in step 7. To do this you might have to change where the cables are positioned where they connect to the motor. By adjsuting the 2 nuts on each cable that hold them in position you can lengthen one of the cables and shorten the other.

    I found step 8 to be a royal pain - be patient - to be honest, I haven't yet been able to get them perfect - but I have gained 30 - 40 rpms so far.

    Fuel Sender The black trap door was removed.

    Removing trap door on fuel sender

    Primer Install

    1) Disconnect the red fuel selector switch from the fuel circuit and remove it.

    2) Use the reserve feed siphon tube from the fuel sender for the feed line to the carbs. The reserve siphon tube is longer and provides a more consistent fuel delivery.

    3) Feed the primer with what was previously the main siphon tube from the fuel sender.

    4) For the OEM GP1200R carbs you can disconnected the accelerator pump by removing the cam that activates the pump. You can then use the accelerator pump feed fuel lines and fittings on the carbs with an aftermarket primer kit. For a US ski the accelerator pump only provides fuel to cylinders 1 and 3 so you will need to add a fitting for cylinder number 2. For a European ski the accelerator pump feeds all 3 cylinders.

    5) Mount the primer plunger in the spot the fuel selector switch was in.

    Note: As an alternative to using an aftermarket primer you can simply leave the accelerator pump fuel lines connected to the accelerator pump and manually push on the accelerator pump plunger to prime the ski.


    I am using an old style Riva GP1200R ride plate. Other good choices are the old style R&D GP1200R plate or the new style R&D GP1300R plate.

    Rideplate mods I did:

    - machine (or grind) on the rear mounts, this allow you to increase the angle the plate sits at
    - grind notches in the bottom of the plate so that it will fit around the bottom of the 1300 2 inch pump extension and pump
    - the riding surfaces of the plate are not very flat (crappy quality control) ideally they should be trued flat
    - angle the front of the sides of the plate up (this is Carl's (Island Racing) mod 4 or Jim's FF mod)
    - grind on the leading edge of the plate where the notches for the transom are - see picture shown in this thread (thanks Porksworld) for this one

    For those of you not able to you own rideplate mods there are a couple of shops equipped to provide this service. (Island Racing or Jim's Performance)

    In order for the rideplate to fit, the bottom of the pump and the bottom of the pump nozzle will have to have some material removed to provide additional clearance. This is a simple process and you can do it yourself with a hand grinder.

    Compared to a stock rideplate, a modifed rideplate will add 4 to 5 mph on flat water. This is the single most effective speed mod available for the GPR. Focus on the rideplate angle - this is where most of the speed can be found

    When installing the plate I will be positioning it so the center section of the plate is on a 4.7 to 5 degree angle to the hull. Instead of using angles many people measure the distance the rear of the plate is above the bottom of the hull - the target measurement that many people use is .950 inch.

    At the same time ensuring the sides of the ride plate don't sit lower than the pump shoe and hull. Always check this with a straight edge. It is OK to have a small step up from the shoe to the center flat section of the rideplate. My step, measured at the side of the plate is .020 in.

    Try adding more angle on the plate, do small steps at a time. There is a sweet spot for the rideplate angle and with every plate / ski this spot is different and it is worth trying to find it. When adjusting the rideplate angle you need to use small changes. With my plate I saw a 1.5 mph difference with a .020 in shim on the rear of the ski.

    Rideplate Angle & Pump Shoe Discussion

    Skegs versus No Skegs

    I left the skegs on the rideplate. A rideplate with skegs will corner harder than a plate with no skegs. If the skegs are removed, the ski will have a tendency for the rear of the ski to slide around a corner.

    All things being equal a rideplate with the skegs removed will be faster than a rideplate with skegs.

    Trim Tabs

    R&D trim tabs

    Rear section of trim tab was cut off. This makes the trim tabs the same length as OEM tabs. The R&D trim tabs are thicker and angled that is why I prefer them to the stock tabs.

    Tabs shimmed down .100 inch all 8 mounting bolts. For a more stable ride you can use a larger shim and/or you can add an extra .040 inch shim under the rear mounting bolts (ie .100 in front and .140 inch rear)

    When I use the stock trim tabs I shimm them down with 2 washers under all 8 bolts.

    Filling Pump Shoe and Rideplate mounting holes with epoxy putty


    I use a set of Danny's custom stepped sponsons that he is selling.

    Another option is the OEM sponsons in the stepped position. I prefer my Danny sponsons because they provide improved cornering.

    Stepped OEM Sponsons - 1

    Stepped OEM Sponsons - 2


    I am using a Riva D plate that has had the opening opened up .200 inch. While I saw no top speed gain with this modification I left this mod on in the hope it would raise my low and mid range HP. (Which is really hard to measure using seat of the pants testing.)

    I am using a GP1300R waterbox and sound suppression box. I saw no gain when I added the 1300 waterbox. Others have reported a small gain when they switched to a 1300 waterbox. The 1300 waterbox is quieter than the 1200 waterbox.

    I do not use a free flow. The free flow is very loud and it slowed me down approx. 1 mph.

    I drilled a whole in the exhaust mounting bracket. This allows you to see the tuning T handle on #2 carb.

    Jetworks Mod

    I did not install the Jetworks mod. I find the Jetworks mod provides very little gain and it makes the water lines more complicated which increases the chance of a water leak.

    Riva CDI

    I am using a R&D CDI with a custom R&D BB curve. R&D offers curves they developed for their 1360 big bore motor. These curves work well on high compression (160 to 170 lb) motors.

    With compression this high the Advent 94 or 84 curves have too much timing and they actually reduce your top speed.

    With compression this high a stock CDI would have also been a good choice.

    Air to Motor

    In stock form the GPR motor is starved for air. You can raise you RPMs by allowing more air into the motor area. To fully satisfy the motor air demands it doesn’t take much.

    Air Opening

    Create an air opening on the right hand front cowling (to match the left hand cowling). Use a sharp exacto knife and cut away the black plastic as shown above.


    Storage Bucket

    I have also cut holes as shown above in the inside layer of the windscreen and in the top of the storage bucket. If you don’t want to make the holes in the storage bucket you can simply remove the storage bucket and leave it at home when you do speed runs. I have 2 storage buckets, one with holes and one without. I use the storage bucket without holes on rough water days when I am concerned with water intrusion.

    Do not cut holes in the windscreen and storage bucket if you ride in the surf.

    Steering Nozzle

    Protec nozzle - 9 mm longer than OEM - same diameter as OEM - oh yeah it is metal so it won't break like the cheap plastic OEM nozzle

    Protec Nozzle Test

    The cheap crappy stock one works fine - it just breaks and that was the reason I replaced it - I saw no speed gain from the Protec nozzle.


    Delta VForce II reeds. While no custom spacer plate is required I am using a spacer in an effort to improve reed life.


    OEM carbs with the following jetting

    Pilot 120
    Main 130
    N/S 2.0
    95 spring

    Accelerator pump disabled. I disabled the accelerator pump by simply removing the cam that pushes on the pump. The choke plates were removed.

    I intentionally used this jetting which is rich on the low end. My thinking was it would facilitate cooling the motor down between speed runs. Despite being rich it still runs clean throughout the complete rpm range.

    I have also been using a set of Novi carbs. My jetting for the Novi's is

    Pilot 120
    Main 135
    N/S 2.3
    115 spring (I tried 95 and it loaded the motor up)
    95 restrictor jet

    Intake Manifold

    When using Novi's you have to ensure the carb bodies are aligned with the openings in the intake manifold. In most cases to get this correct you have to elongate the mounting bolt holes in the carbs a bit so you can slide the carbs to one side.

    Oil block off plate

    Oil pump was removed and a block off plate was added. The oil send was removed from the tank and zip tied upside down to the gas tank straps. (oil sender gauge now reads full)

    Pump Plug Kit

    After installing a PPK you should take a long straight edge and see if the pump shoe is sitting down below the hull line. If it is, it needs to come off and be reinstalled. When I install the PPK I do not use the rubber pieces that sit in the holes in the bottom of the shoe. (this way I never have the problem of the shoe sitting too low) When sealing the shoe to the ski I focus my effort on ensuring the large gap between the pump shoe and the transom is filled with fast cure 3M 4200 or 5200.

    I make sure the shoe and hull mating surfaces are completely clean. I remove the foam strip across the bottom edge of the shoe - it always comes off eventually anyway. Use rough grit sandpaper on the shoe and the hull to get a proper bond. Before applying the 3M I clean everything using carb cleaner, acetone, 95 % alcohol or some really good cleaner. Wear vinyl gloves and use masking tape on the hull and shoe to keep excess silicone off the hull.

    When mounted, I want the shoe to be recessed up into the hull. I found the sweet spot to be a range between .05 to .07 inch. By this I mean the shoe riding surface is .05 to .07 inch higher than the bottom of the hull. Incidentally .070 in this happens to be the thickness of a nickel.

    Intake Grate and Shoe

    I am using an OEM pump shoe properly sealed with a modified Worx double bar intake grate.

    I no longer use R&D double bar intake grates on my skis because there have been to many instances where these grates have broken.

    The intake grate has been blueprinted so it fits the shoe properly.

    The following paragraph on Intake Grate Blueprinting is courtesy of 2FAST4U

    "When you have your pump shoe out bolt the intake grate to the shoe and match the grate to the shoe by grinding the shoe and grate till they match exactly on the inside as well as under side. The fit of the grate to the shoe is very bad. I also do a second grate (Spare) Since a purfect match can't be done once the shoe has been sealed in. Also when sealing the shoe and transom plate in I use muratic acid to ecth plate and shoe so the sealer will stick to both good. The proper sealing of the shoe and transom plate is a must for a super fast ski."


    It is not safe to use the OEM intake grate on a modified GPR.

    Comments on OEM intake grate

    Impeller and Pump

    I am using 2005/2006/2007 GPR pump.

    The impeller pitch I am using is Dynafly 15/25 SB. Impros pitched the impeller. All blades are pitched identically.

    I do not use an impeller nose cone.

    For this motor a 15/25 pitch is a little too high. I have also tested using a Dynafly 14/22.5, whick was too low. With the 15/22.5 my rpms went up but I lost .5 mph. A 14/24 would probably be the ideal pitch.

    Pump Nozzle

    With a 2005 GPR pump I am using an 85 mm GP1300R nozzle. With this unported motor the 85 was faster than the 87. Some skis with more HP may require using an 87 mm nozzle.

    I added an electric bilge pump and I removed the pump nozzle siphon tube.

    To provide clearance for the angled rideplate the bottom of the nozzle had some material removed using a hand grinder.

    GP1300R 2 Inch Pump Spacer

    I upgraded my GP1200R to the 1300 set-up. (both 05 pump and 2 inch spacer)

    Pump Tunnel

    I have reinforced the pump tunnel. To do this I used layers of fiberglass cloth and Epoxy resin. With the SMC hulls any glue or resin used must be epoxy based in order for it to stick to the hull. Note: if you are using a 2003 or newer hull I would suggest you use the R&D carbon fiber tunnel reinforcement kit or use a fiberglass tunnel reinforcement kit.

    Modifications I didn’t do

    There are a bunch of mods that you sometimes see suggested that I didn't do on this ski because my testing has shown they do not provide any speed gain.

    Power core
    Stinger I, II or III
    Modify transom in anyway
    Use Seadoo coils
    Free flow
    Pump cone
    Impeller cone
    Double or triple fuel sender
    Double or triple cooling

    My closed course handling set-up

    I often ride in really rough water on Lake Ontario. I often see 2 to 3 ft chop. I also enjoy running around a CC race set-up. This is the ski set-up I use when having fun in these conditions.

    Shred master rideplate
    Bullet trim tabs cut to fit
    XL1200 pump nozzle
    R&D Pro pump shoe and matching single bar intake grate
    R&D auto-drop nozzle
    Danny's stepped sponsons
    Skat-trak 14 vein setback pump
    Skat full swirl 16/24 impeller

    Until you have ridden a ski in rough water set-up like this you can't appreciate just how good a GPR can handle.

    If you don't want to use the more difficult to find parts that I use on my ski, here is a comparable set-up I would recommend:

    Stock rideplate
    Riva or R&D trim tabs shimmed down 2 washers all 8 bolts
    XL1200 pump nozzle
    Riva or R&D single or double GP1200R/GP1300R intake grate
    R&D auto-drop nozzle
    Riva or R&D sponsons
    2005 GP1300R pump, pump cone and o-ring
    Skat full swirl impeller

    The following links are for various test results I have posted over the years.

    Test Results - Misc

    Test Results - Rough water set-up

    Test Results - Shimmed Trim Tabs
    Last edited by philip_gpr; 03-15-2008 at 10:52 PM.

  2. #2
    Crash Test Dummy Smitty's Avatar
    Join Date
    Jun 2006
    Cullman, AL
    Good post, Phillip, lots of good info! So when do we get to see some numbers?

  3. #3
    philip_gpr's Avatar
    Join Date
    Dec 2005
    I am still working on trying to get this unported 1300 to 80. I actually do most of my testing with the ski bolted down to the water. Where I ride, Lake Ontario, it is always rough so I have to have the ski planted. I am 1.5 to 2 mph faster than last year so I am making progress. One of these days I will put the speed stuff back on and see what she will do.

    Here is the set-up that is currently on my ski:

    Shred plate
    R&D tabs heavily shimmed
    Modified worx double bar 1200 grate
    Danny's sponsons backs with Beach House Blades
    87 mm 3 degree nozzle
    Protec steering nozzle (soon to be R&D VTS auto-drop)
    I also have a setback 14 vein Skat pump I sometmes use.

    Now with this set-up the handling is amazing - this is a true rough water set-up.

  4. #4
    Chrisrokc's Avatar
    Join Date
    Apr 2006
    Oklahoma City, OK
    Wow, nice! I am going to try and do the powervalve thing soon.

  5. #5
    flyboy's Avatar
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    Nov 2005
    Destin, FL
    can you explain a little more in detail. the FF/island racing 4 rideplate mod. I'm lost.

  6. #6
    Robsauto2's Avatar
    Join Date
    Aug 2005
    Oceanside, CA.
    philip, any reason you chose the pv cylinders instead of the later non-pv cyls?

  7. #7
    Join Date
    Feb 2007
    Cape Town, South Africa
    Can you please provide more detailed information on the Rideplate mods which you have done.

  8. #8
    philip_gpr's Avatar
    Join Date
    Dec 2005
    On a 1300 motor, if you have the choice, the PV cylinders will make more mid range HP. On this ski I am using an unported motor and I am amazed at the get up and go it has.

    On my 1500 that I am building I went with non PV cylinders. With larger bore motors the need for the PV diminishes. In 2004 I had a 1360 motor (which I never should have sold which is another story) and with the PVs manually set open it would still pull hard from a standing start.

  9. #9
    Himes's Avatar
    Join Date
    May 2006
    San Diego

    Thanks, Philip!

    Speaking for the collective, we all thank you for your hard work in figuring out what works and what does not, Philip. Additionally, summarizing all of what you found in an easy to read write up written articulately makes things easier for all of us who just want to go faster without having to parse through nonsense and speculation. The fact that you have limited time to test because of your location makes it even more incredible.

    Just awesome work, Philip!

    I need to get busy on some of this stuff!

  10. #10
    mrbtd's Avatar
    Join Date
    Jul 2005
    Lindenhurst, Illinois, United States

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