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  1. #1

    Question Yamaha gp1200 1999 leapfroging through moderate wave ?

    Hi I got a ,gp1200 1999 ,new old machine and it keeps jumping and jumping even through moderate waves??? also has no low end power,,
    what the *uck!! ,,I thick that ride plate is to short and comes stock with wrong impelller.
    any info is good!!
    also looses its prime ,,hard to start when cold ?I think it's the fuel check valve??
    Ride on even if it's cold,,, no peguins good sign.


  2. #2

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    Sounds like you have some carb issues

  3. #3

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    Quote Originally Posted by craneman View Post
    .......also has no low end power,,
    .........,,I thick that ride plate is to short and comes stock with wrong impelller.
    any info is good!!
    also looses its prime ,,hard to start when cold .

    Most of the info you got is good already.

    Those boats are known for having good low end power. You did not say if it cavitated or not.... or if the engine stalls or hesitates. An impeller could be the problem, but it could also be your carbs.

    You are right about the stock ride plate. It is to short. Two things to fix the old GP hulls and reduce the porpoiseing: aftermarket trim tabs and a longer ride plate. There is lots of info out there about these two items. Do a search. I am confident that a combination of ride plate and trim tabs will cure your porposeing.

    The choke plates on the 65U engines have some holes in them a little smaller than the size of a dime. Because of that, it is hard for the engine to be chocked.... that is get the engine to draw fuel into the carbs when starting.

    Install an aftermarket primer and your starting problems will go away. A reminder: there is a proper way to install an aftermarket primer. There are many threads on this as well.

  4. #4
    Yamaha artisan Cutlass's Avatar
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    The 99 ride plate sucks, try an R&D pro series. XO impeller for a mostly stock engine. A scoop style intake grate will also help keep the pump loaded up with water and keep you planted. The 99 hull doesn't require the big trim tabs like the earlier ones, but there are smaller tabs out there for the 99 hull.

  5. #5
    Yamaha artisan Cutlass's Avatar
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    Also, if you end up needing more porpoise reduction, you could try a '97 GP1200 zero degree exit nozzle. Your 99 has a 5 degree nozzle which pushes the bow up and can cause more porpoising.

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