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  1. #1

    Join Date
    May 2011
    st.louis mo

    Gpr1200 loses speed and power after extended wot

    Like title says just did a bunch of carb work but this is still a problem seems like a fuel issue. Has any had this problem? Will removing the flap and doing clunker mod help?this happens even with a full tank of gas

    ski mods
    stinger 3
    high flow exhaust no water box
    was running with air lid off

    carbs have
    1.5 needles and seats
    120 mains
    110 polits
    95 gram springs
    in carb filters cleaned

    t handles
    7/8 low
    1.5 high

    pulls good
    if at wot for a extended amount of time it drops the front noise and feel noticeable lose of speed

    Any info will help
    thank you

  2. #2

    Join Date
    Aug 2006
    I had a simular problem on my GPR, the fuel line(reserve line) in the tank column actually grew longer, pressing against the flapper at the bottom and starving the engine for fuel when running hard. Might want tocheck the tank system real good.

  3. #3

    Join Date
    Jan 2006
    Texas City, Texas
    Quote Originally Posted by crittpen View Post

    .........if at wot for a extended amount of time it drops the front noise and feel noticeable lose of speed

    thank you

    This is an indication of a lean condition. When at wot the cylinder is running lean, the piston heats up, expands and rubs hard against the cylinder. The hard nicasil cylinder will save your bacon for a few episodes of this, but not forever. I'm not saying that this is your problem, but that it potentially is.

    Sears sells a "bend-a-light" that has a shaft so small that you can easily pull the plug, bend and insert the light and inspect the cylinder/piston when you are in a dark room. I did this and found that the piston was actually being heat blasted and was erodeing away nearest to the exhaust port. The light will not show you what a borescope or pulling the cylinder head will show, but it is less time consumeing and cheaper if you know what you are looking at. I wound up replacing #1 piston before it grenaded then rejetted the low speed jets (bigger).

    Other people, I understand put a low speed jet in the common carburator fuel return line to help build back pressure in the carbs so that more fuel could be delivered under higher pressure through the same jets. I belive a 100-110 low speed jet was the standard.

    Also, pressure that is created in your fuel tank from the fuel may be reduced a bit when you get to a low tank level. As a result of that, fuel delivery may be reduced into the carburators as your tank level falls.

    Mark from RPM racing (God rest his soul) lost a race at Catalina Island because of this issue years ago... he lost a cylinder.

    I'm not saying that this is your problem, I'm saying that it sure sounds familiar. Get that light and inspect the inside of your cylinder for deep scratches and the piston for any unusual wear near the exhaust port and in the very center of the piston. Also, check piston color..... it should not be black.

  4. #4

    Join Date
    May 2011
    st.louis mo
    wow yeah my reserve line grew so much it poped the unscrewed side of the screen and flapper out i cant even put it back on
    I am going to run it like this for the weekend to see if that was the problem while I wait on the cluckers to come in

    Looked in the spark plug holes cant tell much with out the proper light but the tops of the pistons are black
    I havent ran it long since I rejeted the carbs
    Probaly about 35mins

    ski now has 97 hours on it
    i bought it used with the stringer 3 exhaust not sure how long it was ran with that on there

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