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  1. #1

    87 650 sx runs ruff at idle

    can anyone give me some suggestions to help fix my ski its an 87 650sx it seems to run fine when im on the throttle but when its at idle it runs real ruff and usually dies out the motor seems to vibrate real bad. ive tried cleaning the carb and playing with the idle screw i just cant get it to run right


  2. #2
    seaobin's Avatar
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    have you checked the cylinder compression? If you have low compression, at low idle, the jet pump can create enough strain to cause that.

    Also, Check you piston wash and see if that give you a clue as to weather you are running lean or rich

  3. #3
    i ran a compression test and was at 180 psi in both cylinders. what would i look for when checking piston wash? it has alot of modifications done like reed spacers high comp. head and pipe would that cause it to run ruff at idle? it was running lean before because the previous owner did not have gaskets on the carb or reed gaskets i got that fixed and all the other gaskets look alright

  4. #4
    seaobin's Avatar
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    so ddi you change carb settings? It is possible you are very rich now.

    If you are going 5 mph and pin the throttle what does it do?

    1) Jump out of the water and then fall on its face
    2) Blubber like you are guzzling water
    3) Run fine

  5. #5
    seaobin's Avatar
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    180 PSI what kind of gas are you running? 93+ octane with a splash of racing fuel or octane boost??????

  6. #6
    seaobin's Avatar
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    Piston Wash

    get a small flashlight from ACE hardware with a flexi shaft. pull the plugs and in a darkened place (under a towel, in the garage, etc) Move the piston to BTC and look at the piston crown

    1) Dark Brown and Dry--Lean
    2) Brown, wet and small silver spots around the edge--good
    3) Silver on more than 30% of piston and oily or wet looking--Rich

  7. #7
    Quote Originally Posted by seaobin View Post
    so ddi you change carb settings? It is possible you are very rich now.

    If you are going 5 mph and pin the throttle what does it do?

    1) Jump out of the water and then fall on its face
    2) Blubber like you are guzzling water
    3) Run fine
    it will bog around for a while and die out it wont produce enough power to plane out.i changed the jet settings back to stock im going to see if that helps next time i get a chance to take it out

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