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Losing vacuum operated petcock?

Discussion in 'XJ Technical Chat' started by SteelMan, Jul 21, 2014.

  1. SteelMan

    SteelMan Member

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    Hey Everyone,

    I was cleaned my gas tank and while stripping it I was debating on switching the petcock out for a gravity fed vs the stock gravity fed one. I have been doing some research and some people say not to do it and just ad a inline petcock, other people say its fine and not to worry about it. Does anyone have a opinion on this?

    I have a 83 Seca 750.

    Thanks,
    Mike
     
    SteelMan, Jul 21, 2014
    #1
  2. bmarzka

    bmarzka Active Member

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    IMO a petcock is a second defense against flooding the crankcase. If the floats are set correctly and working properly, it doesn't matter what petcock you use.
     
    bmarzka, Jul 21, 2014
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  3. XJOE550

    XJOE550 Active Member

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    Keep the vacuum operated one if it is functioning properly. If you are worried about it failing, I don't see any reliability advantage with a manual petcock vs a vacuum one. They both can fail. But with the vacuum one you have the added advantage of automatic operation. If your vacuum one does fail, then just buy a high quality rebuild kit for it and your'e good for years. Much cheaper than buying one of those manual pingel petcocks.
     
    XJOE550, Jul 21, 2014
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  4. rocs82650

    rocs82650 Well-Known Member

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    The stock petcock does not supply fuel to the carbs via "gravity". When your bike is running with the petcock lever in the "on" position fuel is delivered via "vacuum". Imo rebuild the stock petcock and add a briggs & stratton shut off valve for extra security. Even if you go with a gravity fed petcock add the shut off valve.

    Gary
     
    rocs82650, Jul 21, 2014
    #4
  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Unless ther is a fuel pump in the system, fuel is definitely supplied by gravity.

    The only role that engine vacuum plays is to open an otherwise closed valve in the petcock. Engine off, valve is closed. Engine spinning, valve is opened by vacuum allowing fuel to flow.


    OP,

    Rebuild the factory petcock as outlined here: http://www.xjbikes.com/Forums/viewtopic/t=25058.html

    Once completed you'll have a leak free petcock, and won't need any additional valve (all fuel control valves fail eventually. No point in adding another thing that has to be replaced).

    If there is a concern that fuel will get past the float valves and into the crankcase the thing to do (and the only thing that corrects that problem) is to replace the float needles and make sure the floats are moving properly and are set to the correct height.
     
    k-moe, Jul 21, 2014
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  6. SteelMan

    SteelMan Member

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    Thanks guys! Looks like I will just rebuild the stock one then. Rebuild kits is added to the parts list along with carb rebuild kits :)
     
    SteelMan, Jul 22, 2014
    #6

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