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  1. #1

    loss of rpm and thrust after grate mod.

    Yes, I am new and made a dumb mistake(I need confirmation though).

    Stock 1997 gp 1200 with 120-118-120 compression and will rev to 6900psi plus out of the water. I had some battery issues and while the ski was down I installed a primer kit and cut out the two middle bars of the stock intake grate.

    1.Did I need to adjust the carbs after removing the choke linkage?

    2.Did removing the two center (4 stock) bars from the intake grate really cost me 1500 - 2000 rpms max speed, and loss of thrust?

    What is the recommended intake grate and impeller for this ski in stock form?

    Thanks in advance for the help and suggestions.

  2. #2
    quadzilla's Avatar
    Join Date
    Apr 2007
    LOCH NESS Monster-Land

    Smile ????????

    Hey GP1200TX..

    First up welcome to the forum...

    As for your mods the answer is NO the mods won't have made you lose RPM's...

    The thing here is you say revs to 6900psi(i'm sure you mean rpm) out the water..

    There's NO load on the engine out the water.. so not a valid test at all..

    First thing you need to do is test it in the water.. check your RPM's and speed..

    You'll likely find it is much the same as before...!
    The compression is in the good range..

    In an ideal world you'll have available to use an Aftermarket Tach and a GPS unit..
    To get some baseline figures..

    Was the reason for the primmer kit because of bad starting..???
    If it was it might be time to give your carbs the once over/service..!!
    Also did you remove the choke plates..?? not required with the primmer installed..

    Once last thing who did the work..?? yourself or a shop..???

    If you can list any other mods and your method of testing your ski..??


  3. #3
    I lost about 1,500 rpm according to the factory tach. I removed the choke assembly when I installed the primer kit. Prior to the intake grate mod and primer kit I was at 6,900+/- rpm in the water according to the factory tach.

    Aside from rebuilding the carbs, which I will look into, would the removal of the choke plates require a re-jet due to the increased airflow?

    The ski "bogs" under full throttle acceleration now. Prior to the changes this did not happen.


  4. #4
    Yes, the primer kit was due to poor cold starting, especially after idle for a few days-week.

  5. #5
    quadzilla's Avatar
    Join Date
    Apr 2007
    LOCH NESS Monster-Land



    Ok its seems your carbs are a likely candidate for an overhaul..!!

    For the hard starting:..
    My first guess would be knackered check valves in the carb fuel pumps..
    Excessive cranking on the starter is known to screw them up..

    Fairly easy job.. although it does require the carbs to be removed to do..!!

    With the choke plates removed.. you may need to fatten up the jetting a little..

    When you say the ski bogs under full acceleration is this from a dead stop..???
    Also by bogs down, Do you mean the engine dies down OR does it just rev its nutts off and go nowhere..???
    Does it pull smoothly from a slower squeeze on the throttle..???

    AS For the factory tach... Thats a waste of time.!(too hard to read on the move)
    Its Not any better than the dreamometer.(speedo)

    If you can, buy or borrow a tach and GPS unit.. (gps not so important)


  6. #6

    It bogs from a dead stop. The ski normally takes about 1 minute to warm up enough to hit wot and not bog at all. Now even after a half hour the ski bogs(I would NOT say it revs freely, not like it used to). I was on a lake in rough chop (1-2') and I used to be able to time the jumps with the throttle and get instant acceleration. Today it just felt like I did not have the throttle response when the motor was under a load. When the back of the ski came out of the water it reved to higher rpms without any issues and when the pump would load back up the ski lost the rpms.

    Maybe it was the slower overall speed, but I felt like the ski was hooked up better, just not the same power or rpms.

  7. #7
    Me Hahn and Joe H204YOU's Avatar
    Join Date
    Jan 2006
    Panama City Beach Florida
    Just a couple of quick checks for you.A-are you sure you are tapped into the correct fuel line for the primer?B-have you inspected the pump/impellor area for fishing line-rope-or vegitation?This has been found by many to load the motor.

  8. #8

    The fuel line I tapped was the reserve (original line and said "res"). I just double checked the pump housing/driveshaft/impeller/ etc. and everything is clear and free of damage. When I first got on the ski I checked the impeller/housing for vegitation etc. because it felt exactly like something was clogged in there.

    Is there any possible way removing the two center grates without completely grinding everything smooth would cause my problem? Could I just be over loading the pump, causing a reduction in rpms?


  9. #9
    quadzilla's Avatar
    Join Date
    Apr 2007
    LOCH NESS Monster-Land

    Question ???

    Is there any possible way removing the two center grates without completely grinding everything smooth would cause my problem? Could I just be over loading the pump, causing a reduction in rpms?


    It might be time to do a compression check..!!!
    Will only take five minutes and will give a good idea whats going on with your motor..!!!

    After that it could be needing a carb rebuild..!!


  10. #10
    One more thing, not sure if it helps, but I went through fuel like a hot knife through butter. I also used a lot of oil. I really only rode for about 30 minutes and went through 3/4 of a tank of gas. Normally this would last about an hour and a half with much faster speeds and for much longer duration.

    I probably only rode a few miles, up and half of Lake Conroe once. Writing this tells me the ski is very rich and this caused the poor mileage and bogging. But, I think I tried slowly increasing the throttle once or twice and ended up with the same reduced speed and rpm. Would the carbs just all of a sudden go from normal to full rich (too much fuel)? The removal of the choke plates would cause the ski to run lean at worst right? I believe this to be true because of the fatter jet recommendation.

    Anyone have an estimate for rebuilding the carbs?

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