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PetCOCK!!

Discussion in 'XJ Technical Chat' started by Ben Francis, Jul 28, 2016.

  1. Ben Francis

    Ben Francis Member

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    My XJ 550 project bike was running great and all of a sudden started running like a (see the thread title). I cleaned the carbs and it ran okay for a few days then went back to running like crap. Well today after making sure my carbs were in sync and the electrical things were all sorted. I dumped the and and found that the petcock doesn't let fuel flow evenly but when the pet cock was turned to prime it flowed fast and a lot. So I put everything back on and rode it with the pet cock on and it died within minutes but then I put it on prime and it has ran great ever since... Is it simply just a busted petcock or could the vacuum hose have some say in my problems?
     
    Ben Francis, Jul 28, 2016
    #1
  2. k-moe

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

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    The vacuum valve isn't opening much if at all. The vacuum line could be cracked. Start by replacing it with new vacuum line.
     
    k-moe, Jul 28, 2016
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  3. Ben Francis

    Ben Francis Member

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    I have taken this line off and made sure it was clear and clean and its practically new hosing
     
    Ben Francis, Jul 28, 2016
    #3
  4. k-moe

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

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    Practically new, or you-put-it-on-yourself-new?
    Vacuum hose can look fine, but become porous as it ages. Replacement is cheap, and will rule that out as a cause.
     
    k-moe, Jul 28, 2016
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  5. Ben Francis

    Ben Francis Member

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    I just want to make sure we are talking about the same thing. (I am relatively new to street bikes and four strokes, I was raised around two stroke dirt bikes) This is the hose that runs from the petcock to the flange on the cylinder right?
     
    Ben Francis, Jul 28, 2016
    #5
  6. k-moe

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

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    Correct.
     
    k-moe, Jul 28, 2016
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  7. Ben Francis

    Ben Francis Member

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    Alrighty! I will buy some new line tomorrow and see if that helps if not Ill get back to you! Thanks!
     
    Ben Francis, Jul 28, 2016
    #7
  8. cgutz

    cgutz Well-Known Member

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    If that doesn't solve it, the diaphragm in the petcock may not be working. Rebuilding is easy. Get the kit from XJ4ever (top right link on this page).

    Here are the step by step rebuild instructions: http://xjbikes.com/forums/index.php?threads/25058

    I rebuilt mine this summer, and works like a champ.
     
    cgutz, Jul 29, 2016
    #8
  9. Nuch

    Nuch Well-Known Member

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    Also consider that not all hose are made equal... (chuckle). A new piece of fuel line (or windshield washer tubing, etc.) will not do for instance. You need something that is specifically made to withstand the suction that is created and therefore will not collapse from the pressure. Vacuum line that I purchased from XJ4ever (again top right hand corner as cgutz suggests) has significantly thicker walls to prevent just that. I rebuilt my petcock as well. It's been over a year now of problem free service.
     
    Nuch, Jul 29, 2016
    #9
  10. Ben Francis

    Ben Francis Member

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    Thanks guys, I bought some new line today, and put 60 miles on the bike, petcock set to on and it runs great!
     
    Ben Francis, Jul 29, 2016
    #10
    k-moe likes this.

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