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Thread: Whats up with my 90??

  1. 06-01-2007, 10:48 PM #1
    70ATC90's Avatar
    70ATC90
    70ATC90 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Question Whats up with my 90??

    I have an almost totally stock 1978 ATC 90, all it has is a cobra exhaust and a K&N air filter. The carb I have isn't stock, its a reproduction one I got from DrATV. It has been running really rich even though I have the fuel/air mixture screw set pretty lean. It runs well and I can almost get it to idle but whenever I give it any throttle it bogs down and dies. I have tried many things, I lowered the needle as far as it will go and I changed from a size 82 main jet to a size 70. What else can I do? I have an intake on it from an atc 110, could this be the problem?
    1978 ATC 90
    2001 400EX


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  2. 06-02-2007, 12:03 AM #2
    bigreddaddy's Avatar
    bigreddaddy
    bigreddaddy is offline Just Too Addicted Arm chair racerJust too addicted
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    How can it run well if it doesn't idle and dies when given throttle? Pull your spark plug and post it's condition.

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  3. 06-02-2007, 02:32 PM #3
    70ATC90's Avatar
    70ATC90
    70ATC90 is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Quote Originally Posted by bigreddaddy View Post
    How can it run well if it doesn't idle and dies when given throttle? Pull your spark plug and post it's condition.

    picture this... black, sooty, carbon covered... like what a rich fuel mixture usually does to a spark plug...
    1978 ATC 90
    2001 400EX


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  4. 06-02-2007, 02:57 PM #4
    Daddio's Avatar
    Daddio
    Daddio is offline Power User Roostin Away
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    Has there been any work done to the engine lately? How old is your plug? If it has points are they in good shape and properly adjusted? If you don't have good spark it may appear to be running too rich.
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  5. 06-02-2007, 06:30 PM #5
    03 ORANGE SHEE's Avatar
    03 ORANGE SHEE
    03 ORANGE SHEE is offline Power User Got the holeshot
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    air/fuel screw only works up to 1/4 throttle
    main jet does 3/4 throttle and up
    needle works 1/4 to 3/4 throttle
    maybe this helps you...
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