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  1. #1

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    2001 Yamaha GP800R accelerator pump

    I finally was able to rebuild my carbs but had trouble connecting them together. Not sure If I did it correctly...

    Anyways, I was able to reinstall everything and put the exhaust back....I was so happy it started right up. I stopped it and put back the silencer case. After that, it wont start...

    its totally flooded, when I removed the spark plugs and hit the start button, tons of gas shoots out from both valves....does that mean I have a leak on both carbs ( maybe needles are stuck on both carbs)

    What does the accelerator pump do...in an idle position, is the lever suppose to be in a decompress position and in full throttle, its in compressed position...Did I put it back wrong...

    attached is the accelerator pump diagram...
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2

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    It sounds like your N/S arm is holding the seats open, allowing fuel to pour in.

  3. #3

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    Quote Originally Posted by Jonesyfxr View Post
    It sounds like your N/S arm is holding the seats open, allowing fuel to pour in.
    Dumb question, is the lever I mentioned in my question the N/S arm you are referring to...its the lever that compresses and decompresses a button on the accelerator pump...

    Another test I did today was hold the throttle in full throttle position....it seems to stop leaking gas....only some gas shot out from the spark plugs valves when I hit the start button...

    In full throttle position, the arm compresses that accelerator pump button....can someone confirm I did this wrong or right...thanks

  4. #4

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    I think I got my answer. Per the video, the throttle was fully open and the lever was in a decompress position...when he moved it to idle position, the lever was in compress position...

    if anyone can confirm, I'm ready to tear it apart to fix

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  6. #5

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    disregard the previous reply, I was wrong...

    today, I removed the carb rack and inspected the throttle mechanism...its reconnected properly, and so is the accelerator pump arm...im lost now why the engine is flooded...

    can someone tell me if one carb is leaking, would it flood only in one cylinder or both... if I remove the spark plugs, would gas shoot out on only one valve???

  7. #6

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    Pulls the carbs apart and check the N/S arm. It maybe holding the N/S open

    Also make sure you pressure tested the carbs. Chances are you would’ve found this issue if you tested them.

  8. #7

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    Quote Originally Posted by Jonesyfxr View Post
    Pulls the carbs apart and check the N/S arm. It maybe holding the N/S open

    Also make sure you pressure tested the carbs. Chances are you would’ve found this issue if you tested them.

    This is my first time rebuild a carb or any carb...I did wonder if there was a test to test for leaks...

    after your comment, and more research, I should have done the pressure test

    just ordered the pressure tester and will let you know how it goes

  9. #8

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    went to harbor freight and made my own pressure tester....did pop off test on both carbs....both did not pop, went as high as 45psi only....one did bubble but fixed it by replacing o-ring on seat....

    both had leaks on the fuel pump when I applied pressure higher than 10 psi....I rebuilt it with new kit on one of the carbs but its still leaking...

    how do you keep those plates from leaking when putting them back...should I use some liquid gasket???

  10. #9

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    after more research, leak is probable from cheap rebuild kit from ebay from 5 yrs ago...will buy mikuni rebuild kit to see if leak goes away...

    if my thinking is wrong, please let me know....currently, its leaking on fuel pump side when I apply about 20psi....is that normal since leak test calls out for only 10PSI...

  11. #10

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    YouTube how to pressure test Mikuni carbs.


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