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vac line on petcock

Discussion in 'XJ Technical Chat' started by cruzmystar, Sep 8, 2006.

  1. cruzmystar

    cruzmystar Member

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    just got an 85 xj700. i had overheard in another post that the line coming off the diaphram on the petcock should be hooked to manifold vacuum. mine has been plugged off by someone. i'm guessing from what i read it's due to the diaphram being shot but my question is what is this diaphram for? function?

    thanks

    nick
     
    cruzmystar, Sep 8, 2006
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  2. Robert

    Robert Active Member

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    The diaphragm is used to switch fuel flow only upon a vacuum signal from a running engine. No vacuum from the carbs, no fuel is supposed to flow. Keeps the carbs from drownding. Hope that was your answer.
     
    Robert, Sep 8, 2006
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  3. cruzmystar

    cruzmystar Member

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    yep, that's the answer i was looking for. now what is the prime spot for then? is that just free flowing all the time? if you run it in prime all the time will the reserve still work as needed? thanks for you reply
     
    cruzmystar, Sep 8, 2006
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  4. Hvnbnd

    Hvnbnd Active Member

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    PRIME IS STRICTLY FOR FILLING THE FLOAT BOWLS WHEN THEY ARE EMPTY.
    RUN IS THE POSITION THAT THE VALVE SHOULD BE IN FOR NORMAL OPERATION.
    RES IS OF COURSE FOR THE LAST BIT IN YOUR TANK WHEN YOU RUN OUT.

    THE DIAPHRAM IS SPRING LOADED AND IS ONLY SUPPOSED TO OPEN WHE VACUUM IS ON IT.
    THE VACUUM HOSE HOOKS ONTO #2 INTAKE, (BEFORE THE CARB)

    THESE BIKES WERE DESIGNED TO NOT HAVE THE FULL WEIGHT OF A TANK OF FUEL FORCING AGAINST THE FLOAT VALVES WHEN THE BOWLS ARE FULL AND THE VALVES ARE CLOSED. (ENGINE NOT RUNNING)

    GOOD LUCK
    MIKE
     
    Hvnbnd, Sep 8, 2006
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  5. cruzmystar

    cruzmystar Member

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    alright, thanks. looks like i need to get a rebuild kit or a new one comin. fuel comes out of the vac line and the bike runs without it hooked up and the valve in the on position. somethings messed up! lol. thanks a lot

    ~nick
     
    cruzmystar, Sep 8, 2006
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  6. Hvnbnd

    Hvnbnd Active Member

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    Sounds like someone might have cobbled it up to get by... but it still needs to be fixed or sooner or later it will let you down.
    Good Luck
    Mike
     
    Hvnbnd, Sep 8, 2006
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  7. cruzmystar

    cruzmystar Member

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    thanks for the help
     
    cruzmystar, Sep 8, 2006
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