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  1. #1

    99 GP1200 Ride Plate Question

    Hello, I am new to the board and new to jet skis entirely. I just bought a 1999 yamaha GP1200X 2 seater and I am having some porpoising issues. I have spent the past two weeks researching this matter on this board after taking my ski out a few times.

    I normally ride in bay water that tends to have a light chop to (1 to 2)ft waves at any given time with me +1 riding. When riding my ski it hops and bounces horribly in rough water. I can not get over 25 mph comfortably. The ski currently has an older style Riva ride plate. I want to swap it out with a better unit and I am looking for advice from those who know first hand which of the aftermarket plates on the market is a better fit for my kind of riding. Also, what are my limitations/expectations with this ski?

    the ski current has:

    Riva ride plate
    Riva quick-turn nozzle
    Some non OE intake grate
    Riva pro-series adjustable spoosons
    UMI steering

    If I am leaving any details out, let me know and I will post up replys.


  2. #2
    Budman's Avatar
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    I heard that riva made a plate called a goofy plate that was bad as far as porpoising. You may have this one. I would get a newer riva plate or a shredmaster plate. Shim the back of the plate with a couple of stainless washers on each of the back two bolts. Also put your sponsons in the lowest position. Also a set of pro-tec trim tabs will help some. Set your nozzle trim in the neutral or bow down position. Mine porpoised all the time till I did these mods and now the porpoising is gone except when i put the trim all the way to the bow up position. Some people have had to use as many as 4 washers on the back two bolts to bring the back of the ride plate down.

    Budman

  3. #3
    Thanks. I have been looking for a shredmaster ride plate, but unfortunately I think the company is out of business. Their website is non-existent and I can not find a phone number for them. Also, for the trim tabs, I have a 99 and there were no original tabs on them. I spoke with a guy named Pete from Riva and he stated that it wont be a huge pain in the ass to install trim tabs on my 99.

    Last night I ordered a 98 OE GP1200 ride plate b/c it is twice as long as the plate have now. I guess we will see what happens. Today, I took my ski out and added 3 washers to each side of the back. It made a huge difference, but I lost a lot of stability and turning ability. I am going to try a few more things.

  4. #4
    Old Ski Insanity w/rpm500's Avatar
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    Budmans got you on the right course.. post a picture of the plate and we can direct to you to just what it is.. the o/e plates were short and were considered a speed plate...(they sucked in the rough) the groovy was a rough water plate,but its down side is its a speed scrubing plate... try to find a long plate, aftermarket or the longest 'o/e' produced 97 gp plate...on most gp's shim your plate down ,at the rear with approx 4 to 6 washers...(nearly a 1/2 inch).. you will also need longer rear bolts... some 1200 work better with from positive shimming..( i dont think yours as you are running a stock motor, correct me if im wrong, because power has a bit to do with this)

    shread master is no more...I have the texas water cross plate on mine .. its almost as long...


    this being a 99, your hull has been changed from the 97/98's and their need for large tabs..if anything yours could be improved slightly with the small tabs designed to make it better ( they arn't as needed because of that later model hull change)

    also if you dont have one already, a two bar scoop grate will improve the water stability and water processing of your pump..less fall off thru cavitation and unloading from rough airated water...
    I SEE YOU POSTED AS I WAS REPLYING.. PETE SHOULD BE ABLE TO HELP YOU TO SORT THIS OUT SOME!!

    If anything shimming the plate down should force the nose down and make your pivot point more solid for the jet to push against(QUICKER TURN'S)....with sponsons down ,I didnt like the dampening effect they had by scooping and holding onto the water ...IMO, sponsons help streight line stability,but dampen turning abilitys, unless your set up for racing and lean alot using power and 'plant' to stear thru a turn...(set for all around for handleing is why mine are up, not down)

  5. #5
    Quote Originally Posted by w/rpm500 View Post
    Budmans got you on the right course.. post a picture of the plate and we can direct to you to just what it is.. the o/e plates were short and were considered a speed plate...(they sucked in the rough) the groovy was a rough water plate,but its down side is its a speed scrubing plate... try to find a long plate, aftermarket or the longest 'o/e' produced 97 gp plate...on most gp's shim your plate down ,at the rear with approx 4 to 6 washers...(nearly a 1/2 inch).. you will also need longer rear bolts... some 1200 work better with from positive shimming..( i dont think yours as you are running a stock motor, correct me if im wrong, because power has a bit to do with this)

    shread master is no more...I have the texas water cross plate on mine .. its almost as long...


    this being a 99, your hull has been changed from the 97/98's and their need for large tabs..if anything yours could be improved slightly with the small tabs designed to make it better ( they arn't as needed because of that later model hull change)

    also if you dont have one already, a two bar scoop grate will improve the water stability and water processing of your pump..less fall off thru cavitation and unloading from rough airated water...
    I SEE YOU POSTED AS I WAS REPLYING.. PETE SHOULD BE ABLE TO HELP YOU TO SORT THIS OUT SOME!!

    If anything shimming the plate down should force the nose down and make your pivot point more solid for the jet to push against(QUICKER TURN'S)....with sponsons down ,I didnt like the dampening effect they had by scooping and holding onto the water ...IMO, sponsons help streight line stability,but dampen turning abilitys, unless your set up for racing and lean alot using power and 'plant' to stear thru a turn...(set for all around for handleing is why mine are up, not down)

    Thanks alot for the help.
    So far, I have a two bar intake grate. Not sure what brand. I have some type of impeller too. It is not stock. I only looked b/c Pete asked me to.

    The motor is not stock. As far as how much is done to it, I am still unsure. All I am sure of now it Riva Flame Arrestors and it only has 25 hours on it.

    Is there still a way to add trim tabs without major modifications?
    What is the Texas water cross plate?

    Here are pics of the ride plate I sent to Pete. He told me that Riva no longer makes a plate for my ski. They only cut 100 units and once sold they are never reproduced.

    Click image for larger version. 

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    Click image for larger version. 

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ID:	140570

  6. #6

  7. #7

    Porpoising

    I've got a 99 GP800 and I had the same issue. I did the following:
    1. Wave eater clips - apparently a must (a bitch as my manifold bolts did not want to come out)
    2. R&D Pro-Series rideplate with about 3 washers on the back two bolts.
    3. Pro-Tec fixed trim tabs

    One thing is I have not had it in the water yet to test. Will try out this weekend and let you know the results. From the research I've done on this porpoising issue the modifications should improve the handling. The only thing I have not done is put a top loading intake grate on. I'm not sure what the best grate is as I have not looked into them much yet. Anyone have some suggestions?

  8. #8
    Old Ski Insanity w/rpm500's Avatar
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    toploader with the outer wings for its rough water loading ability and then with wings removed, for speed....

  9. #9
    Budman's Avatar
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    This is the plate I have. It is for the 98-99.

    http://www.rivayamaha.com/RivaStore/...0Ride%20Plates

  10. #10
    Quote Originally Posted by jchale View Post
    I've got a 99 GP800 and I had the same issue. I did the following:
    1. Wave eater clips - apparently a must (a bitch as my manifold bolts did not want to come out)
    2. R&D Pro-Series rideplate with about 3 washers on the back two bolts.
    3. Pro-Tec fixed trim tabs

    One thing is I have not had it in the water yet to test. Will try out this weekend and let you know the results. From the research I've done on this porpoising issue the modifications should improve the handling. The only thing I have not done is put a top loading intake grate on. I'm not sure what the best grate is as I have not looked into them much yet. Anyone have some suggestions?
    How hard was it to install the trim tabs?


    Quote Originally Posted by budman
    This is the plate I have. It is for the 98-99.
    How does this plate work for you? Rough Water? Did you have to shim?

    I bought a 97-98 OE long plate just to test it out this weekend to see if it made a difference before buying another performance plate.

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