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  1. #1

    Join Date
    Jul 2013
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    MO
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    yet another newbie

    Hello, I've been into a number of motor-sports; having spent most of my life in more northern climes, I tended to stick to Snowmobiles and ATVs and such. I'm a huge 2-stroke fan and I still have my '84 RZ350, which I ride on occasional track days. I recently purchased a '04 GP1300R from a board member. I've had it out on the water here in MO a few times now and I've been noticing it has a tendency to porpoise a fair but at about 50 and then it settles right down from about 65 on up. I have a 3 minute video of a run I made one morning while the water was relatively smooth on youtube

    I've been trolling the posts looking for ideas and I've read perhaps 50% of the posts my searches have brought up, so please don't flame, I'm working my way through them. I'm figuring it's got a lot to do with me weighing about 70 lbs more than the previous owner and I probably just need to figure out how it wants to be set up for me. I'll post more info as I figure things out.

    I've been told the present performance enhancements are:

    Ben Herman 1390 Big Bore (coated Wiseco pistons) OEM Balanced Welded Crank w/ Hotrod Rods.
    OEM Bearings
    RIVA WFO Head (160psi)
    RIVA Head Girdle
    3-4 Degree Keyway
    VF3 Reeds
    Expanded D-Plate
    Oil Pump Block Off
    WFO Fuel System Upgrade
    RIVA EFI Controller
    FF Speed Ride Plate
    R&D Speed Package Cut Tabs
    R&D Metal Steering Nozzle
    Riva Pump Seal Kit (sealed to speed package specs)
    Greenhulk Stainless Steel 800 Grate
    Riva Free Flow Exhaust
    1200R Waterbox
    Island Racing Holeshot Kit
    2005+ Pump Upgrade with Dynafly Impeller (custom pitched and sharpened, 2005+ spec unknown)
    Carbon Fiber Pump Tunnel Reinforcement
    Tiny Tach (advanced version)

    Any suggestions for things to check for would be appreciated.


  2. #2
    mudslanger's Avatar
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    Jul 2010
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    Huntsville Al
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    1,326
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    Nice setup on that ski. it sounds like it setup for a lot of speed with the plate and tabs.
    Try riding with the trim in the N position if you are running with the nose up and the extra weight can cause it to porpoise at low speeds.

  3. #3
    I've heard there can be water between the layers of the hull.

  4. +1 by:


  5. #4
    YudLuz2's Avatar
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    Jun 2005
    Location
    Flowood MS
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    1,647
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    It looks like it rides very well to me. The little bounce your getting at 50 mph off the throttle is common with a high angle ride plate. It can ride better with me setting up the pump shoe and matching the plate. But most GPR's out there people can't even ride them at that speed because the bounce and slap the water so hard. You could do two things, add a 50 thous. washer to the two rear ride plate bolts, taking some angle out of the plate. Or you could stack some addition washers under your trim tabs. Either way will help with your rider weight, but it will cause a loss of top speed.

  6. #5

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    Jul 2013
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    MO
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    Thanks Ben, I'll try it next weekend. It's really only a problem in the smoother water. However it is at the speed I tend to ride at most (it's one tough to turn beast at 72).

  7. #6
    Julian's Avatar
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    Oct 2011
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    Groningen, Groningen, Netherlands
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    Running great! Nice

  8. #7

    Join Date
    Jul 2013
    Location
    MO
    Posts
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    OK the Riva EFI controller seems to have taken a dump. It got wet and suddenly the machine is super rich all across the range. I've bought a powershot to replace it and read everything I can find on the board that came up in a search for powershot and 1390 and found very little.

    What I'm working with:
    2004 Yamaha GP1300R
    Engine mods:
    Ben Herman 1390 Big Bore (coated Wiseco pistons) OEM Balanced Welded Crank w/ Hotrod Rods.
    OEM Bearings
    RIVA WFO Head (160psi)
    3-4 Degree Keyway
    VF3 Reeds
    R&D Power Plenum F/A
    Expanded D-Plate
    Oil Pump Block Off (running Amsoil Dominator 40:1 pre-mix with 93 pump gas or 50/50 w/av-gas)
    Riva Free Flow Exhaust
    2005+ Pump Upgrade with Dynafly Impeller (custom pitched and sharpened, 2005+ spec unknown)

    any advice you have would be appreciated.

  9. #8

    Join Date
    Jul 2013
    Location
    MO
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    I've been tweaking the power-shot and monitoring the plugs and the pistons with a digital bore-scope, once I figure it out I'll post my results on the fuel controller thread. The porpoising went away after swapping out the 800 grate for an R&D Single Bar Aquavein Intake Grate. It greatly reduced the tendency to pitch the rider off under deceleration as well. I think I lost about 1 MPH, but that's fine as it was faster than I cared to ride (and I can still blow away the monster Bass boats at sunrise). I'm still waiting to install an R&D cone and remove the sump siphon tube from the nozzle (helped noticeably in my XLT running a GP nozzle). Will probably get to it in July, unless the weather continues to be cruddy this weekend.
    Last edited by TailChaser; 05-19-2015 at 07:09 PM. Reason: typos

  10. #9
    Prism's Avatar
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    May 2007
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    "New" Jersey
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    My only advice to you would be to start pig rich on the controller and slowly work leaner until max rpm and response are achieved. At that point I'd richen it slightly for safety....especially with the engine you have there.

  11. #10
    Prism's Avatar
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    "New" Jersey
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    Quote Originally Posted by ZeroClient View Post
    I've heard there can be water between the layers of the hull.
    There defiantly can be. If the ski has ever taken on water in any significant amount, it will seep through the rivets used to hold various things to the hull. (Like engine mounts) I don't know if it will cause more porposing, but I know for fact it can increase the level of "chine walk" at lower speeds. On both my skis I drilled a small hole on the back of the keel near the bottom and threaded a small screw back into the hole as a plug. You'll be surprised at the amount of water that can come out!

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