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Runaway idle no vacuum

Discussion in 'XJ Technical Chat' started by Gcxcountrystar1, Aug 18, 2016.

  1. Gcxcountrystar1

    Gcxcountrystar1 Member

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    I just picked up a 1985 yamaha xj700 when the bike fires up a runaway idle takes over so we turn it off. I have 2 buddies that love bikes one says that we need block some connections on the carbs and my other friend says that there needs to be 4 12 inch fuel hoses that connect to the carbs and just hang . They can't agree on when connection for the vacuum line on the petcock to where on the carbs. can anyone please help me.
     
    Gcxcountrystar1, Aug 18, 2016
    #1
  2. Stumplifter

    Stumplifter Well-Known Member

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    I am not familiar with the XJ700 but the idea of 'vent' tubes rings a bell on at least one of the XJ models.
    Best case scenario for you is to post some pics of your current setup.

    Because you are new I believe you have to have 5 posts made prior to being able to attach photos.
    Add a few quick relevant replies and then post a few pics - there are a lot of wise, helpful folks here that will be able to provide you with the correct answer.
     
    Stumplifter, Aug 18, 2016
    #2
  3. Gcxcountrystar1

    Gcxcountrystar1 Member

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    Thank you
     
    Gcxcountrystar1, Aug 18, 2016
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  4. Gcxcountrystar1

    Gcxcountrystar1 Member

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    I will get my post up and then post pictures when I am able to
     
    Gcxcountrystar1, Aug 18, 2016
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  5. Doubleyoupee

    Doubleyoupee New Member

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    It doesn't matter if you block them or connect hoses to them.
    Pretty much all carbs have a vacuum port, usually on the top but sometimes on the sides. These are just open holes that come out just after the throttle valve (so engine side).
    These ports are used to sync the carbs, but more importantly one of them goes to the fuel petcock (if you have a vacuum petcock) to open the petcock when the engine is running.
    The other 3 of the ports are blocked off. Whether you use a 4-into-1 rubber hose that goes to the petcock, or a single hose to the petcock and 3 rubber plugs on others doesn't matter.
     
    Doubleyoupee, Aug 18, 2016
    #5
  6. Jetfixer

    Jetfixer Well-Known Member

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    either carbs are not in synch ,or you have a huge vacuum leak, or your idle knob needs turned out. Yes this bikes carbs have more hoses.
     
    Jetfixer, Aug 18, 2016
    #6
  7. k-moe

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

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    Not on any of the XJ series.
    You are thinking of the vacuum ports on the intake boots. The carbs don't have any vacuum ports on them.

    The XJ700 carbs have a number of vent/ overflow hoses on them, and one fuel line that goes to the "T" between the two middle carbs. The only vacuum line is from teh petcock to one of the ports on any intake boot. The other intake boots have their vacuum ports capped.
     
    k-moe, Aug 18, 2016
    #7
  8. Doubleyoupee

    Doubleyoupee New Member

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    Yeah you're right. The concept stays the same though :)
     
    Doubleyoupee, Aug 19, 2016
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  9. Gcxcountrystar1

    Gcxcountrystar1 Member

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    Bike is running fine right now it was because of the vacuum line now time to figure out the rear runn8ng light and brake light thank you all for helping
     
    Gcxcountrystar1, Aug 20, 2016
    #9

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