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  1. #1

    Join Date
    Jul 2014
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    6

    Yamaha GP800, any tips on how to keep this thing in the water?

    I have a Yamaha GP800, the ski runs pretty good but in even the lightest chop it will start porpoising really badly. As far as I know everything is stock. The main issue is that at the Lake of the Ozarks its usually pretty choppy and this thing does not seem to handle it all that well. Are there any tricks or modifications that can be done to help smooth out the ride a bit?

    I also seem to have a hell of a time getting it started when its been sitting for a week. Once I get it started then it starts right up the rest of the weekend. Is this typical of a 2-stroke or is there something that could be causing it to not fire up? Have to crank it over and over many times and eventually it fires up, just about the time the battery is about dead.

    Lastly, any fairly inexpensive performance modifications out there that can be done to this ski? I also have a 2012 SeaDoo RXPX that we take out together across the lake, problem is that my wife can't keep up on the Gp800 and I get in trouble for not slowing down for her.

  2. #2
    Quote Originally Posted by Dragunov View Post
    I have a Yamaha GP800, the ski runs pretty good but in even the lightest chop it will start porpoising really badly. As far as I know everything is stock. The main issue is that at the Lake of the Ozarks its usually pretty choppy and this thing does not seem to handle it all that well. Are there any tricks or modifications that can be done to help smooth out the ride a bit?

    I also seem to have a hell of a time getting it started when its been sitting for a week. Once I get it started then it starts right up the rest of the weekend. Is this typical of a 2-stroke or is there something that could be causing it to not fire up? Have to crank it over and over many times and eventually it fires up, just about the time the battery is about dead.

    Lastly, any fairly inexpensive performance modifications out there that can be done to this ski? I also have a 2012 SeaDoo RXPX that we take out together across the lake, problem is that my wife can't keep up on the Gp800 and I get in trouble for not slowing down for her.

    Even tho the power to hull weight on that ski (gp760/gp800) is in your favour, it had design flaws in the hull. Do a search there are tons of info on that. Esentially you will need to at least shim the ride plate in the rear using ss washers to keep the nose down. Riva also made trim tabs for it and adjustable sponsons that help when adjusting them down in the back. The stock one's are adjustable too. Tho hard to find, much of that stuff is still available on ebay. Protec also still has some stuff like ride plates, heads, F/A's, etc.

    That boat won some awards back in the day and the 800 motor puts out great power for a twin. R&D and Group K still has motor mods/kits for it. But the easiest thing to do in the way of increase performance is F/A's, shaved or aftermarket heads, and taller prop. The good news is that the twin is easy to work on... .

    On trick on the starting procedure you can try is crank it for about10sec long enough to energize the pv's and fuel pump, then with it off pump the throttle several times then re-start.
    Good luck and have fun.

    PS: by the way, have you checked your compression (starting problem)?

  3. #3
    I have the same issue on my 2000 Yamaha GP800. I just bought a 1997 GP1200 ride plate as it's longer than my factory piece. they said the longer ride plate helps and then start with two SS washers on each rear bolt and either add or subtract to get it right.
    I also have the factory adjustable sponsons on mine and have them adjusted all the way down and when the water is calm the machine handles like it's on rails but any sort of chop and it porpoises.

    you can pick up a stock 97 gp1200 ride plate on eBay for $30-$40. I just paid $35 shipped for one that looks to be in great condition. also stay away from the Riva "Groovy" ride plates as everything I've read is that they make it worse. most people I've read about either go with the factory 97 gp1200 plate or get an R&D plate and shim it from there. I decided to get a factory piece vs spending triple the money on an aftermarket plate.

    I've also read to get an aftermarket intake grate which would help scoop water and keep it full vs sucking in air. but I'm going to try the ride plate first and see how well that works before spending $150+ on an intake grate.

    as as far as trim tabs go, I haven't had any luck finding any in my searches and nobody makes them anymore for the GP800.

  4. #4

    Join Date
    Jul 2014
    Posts
    6
    Thanks for the advice, I will start looking on ebay for a ride plate. As far as compression, no it has not been checked. When we get the thing to start it runs like a dream, but that first start can be a real challenge after it has sat for a week or 2.

  5. #5
    Myself's Avatar
    Join Date
    May 2007
    Location
    North Central Arkansas
    Posts
    5,048
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    518
    You better check to see if the power valve keepers have been upgraded.

  6. #6
    OzarkYamMonster's Avatar
    Join Date
    Oct 2012
    Location
    Lake Of The Ozarks
    Posts
    2,271
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    Hey Dragunov, where do live or ride @ the Lake ?

  7. #7

    Join Date
    Aug 2021
    Posts
    1
    Hey there,

    I know this is an old post, but I just joined this forum after purchasing a 2000 GP800. Did installing the 97 GP1200 ride plate fix the porpoising issue.? Any other feedback on the installation would be appreciated.

  8. #8

    Join Date
    Jul 2019
    Location
    Buffalo, NY
    Posts
    688
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    Quote Originally Posted by pkbunker View Post
    Hey there,

    I know this is an old post, but I just joined this forum after purchasing a 2000 GP800. Did installing the 97 GP1200 ride plate fix the porpoising issue.? Any other feedback on the installation would be appreciated.

    Welcome!!!

    There are stickies in the 2 stroke section regarding ride plates. We have the R&D extended plate on our 1200R. It scrubs some speed but we hardly pospoise at all, and our lake has a tight chop too. We have a R&D grate as well… we love it.

  9. #9

    Join Date
    Aug 2020
    Posts
    18
    Quote Originally Posted by Myself View Post
    You better check to see if the power valve keepers have been upgraded.
    I second this. Cheap insurance.

  10. #10
    As far as starting. Make sure the gas cap seal is not cracked and actually seals. Make sure the rubber boot holding the fuel pickup is not cracked around the edge. Then I pump the throttle 10 times. It’s always 10 times and the choke pulled out and it starts right away since I do that and fixed the other 2 things. U also need to make sure the accelerator pump is squirting into the carbs. The rear carb always gets blocked. For porpoising make sure the trim is actually holding the nozzle down and it’s not just letting the nozzle move up and down. We had the trim cable stuck and so we disconnected it and tied it in place so it always points down.


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