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  1. #1

    Join Date
    Aug 2007
    Tampa, FL

    Question about fuel pumps

    How do the fuel pumps work on an XL 800 that have pumps as part of the carbs??? What actuates the diaphrams...back pressure from the cylinders? I know they are not electronic or mechanically driven...right?

    Just thinking about my vapor lock and how air filled pumps would not work properly and prevent startup, fuel flow.



  2. #2
    Join Date
    Jul 2007
    Baytown, TX
    The fuel pumps on our carbs are essentialy two one-way check valves with diaghpram in between. The back(air) side of the diaghphram goes to the crankcase of the cylinder, and strokes with the piston. Piston goes up, creates vaccum in crankcase, sucks diaghphram out. Piston goes down, pressure in the crankcase, pushes diaghpram in.

    The one-way valves are just a flap of plastic and rubber over a machined hole.

    If you've got a significant amout of air in your fuel lines, the plastic may not "seat" against the hole, and let air bleed back.

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