Need help with 1987 650SX won’t stay running
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  1. #1
    PWCToday Newbie
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    Need help with 1987 650SX won’t stay running

    I'm at a loss here. I picked up a 87' 650sx and rebuilt the motor, adding new pistons, rings, gaskets and replaced crank with newish one and new seals and rebuilt the carb. Added new primer, but after priming, it runs, then engine will die after a 10-15 seconds.

    It's got an OEM Keihin carb on there, so here’s what I did to troubleshoot

    • Checked all the lines from the tank to the carb for any breaks or holes and for the heck of it replaced main and reserve lines.
    • Took the T fitting out and checked for clogs (blowing in each end, no prob).
    • Took off the pulse line from fuel pump to low speed fitting on carb and saw it pumping fuel when I turn engine over.
    • Checked fuel relief valve and it works
    • Blew back all lines going into tank to make sure no clogs….all good.
    • Checked fuel selector switch by moving to main and reserve by blowing lines and they worked.
    • New primer is pushing fuel to engine.


    What should I do? Can’t get it to stay running.
    Thanks for any help or ideas you guys can give me

  2. #2
    PWCToday Regular drlinklater's Avatar
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    Re: Need help with 1987 650SX won’t stay running

    Not trying to make an obvious suggestion, but is the idle speed screw set correctly?


    Sent from my iPhone using Tapatalk

  3. #3
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Need help with 1987 650SX won’t stay running

    Quote Originally Posted by LBI_Guy View Post
    Added new primer, but after priming, it runs, then engine will die after a 10-15 seconds.
    This is a vacuum leak, most likely at the carb base gasket.

    The primer is successfully starting the engine and opening the needle
    and seat, but because of the vacuum leak, the needle and seat closes
    and remains closed. Then the engine can only run as long as there is
    fuel inside the float chamber. When the fuel inside the float chamber
    runs out, the engine dies.

    Find a new carb base gasket, and make yourself a flat sanding plate with
    a 3/16" thick piece of glass, 220 to 320 sheet of emery cloth, and some
    3M-spray 77.


    Bill M.
    Attached Images Attached Images
    Horsepower == Speed, RPM != Speed



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