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vacum hose to petcock

Discussion in 'XJ Technical Chat' started by jhfrank, Apr 23, 2008.

  1. jhfrank

    jhfrank Member

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    Hi all... quick question... i was starting the bike with the tank vacum tube off. the bike seemed to idle faster, i than attached the vacum hose from the third carb to petcock and the bike would idle down.

    What causes this? it seems that the bike is easier to start when the vacum hose isn't attached to the petcock. (took the petcock apart and it is clean and in working condition)

    Another qustion:
    when i took the carbs apart and put them back together i took the enrichment screws out. i know the manuel says do not play with these as they are set by the factory. What are they supposed to be set at?

    Thanks all
     
  2. switch263

    switch263 Member

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    It idles faster because of the vacuum leaking to atmosphere, not because of anything petcock related, if i'm understanding your question properly.

    if you mean the mixture screws, i believe the factory 'default' (at least for the hitachis on my bike) is 3 turns out from bottom.

    hope that helps
     
  3. Ace_Frehley

    Ace_Frehley Member

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    The bike will idle higher because you have the vacuum open to the atmosphere. However, without the hose hooked up to the petcock fuel won't (or at least shouldn't flow to the carbs) Unless you have it set to 'Pri'.
     
  4. jhfrank

    jhfrank Member

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    Do you know what the physics behind that is? Why would it run faster and than run slower when plugged or attached to the petcock?

    Just curious thats all.

    thanks
     
  5. thefox

    thefox Member

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    Unless you plug the line the engine is now letting air in through the vacuum tube making the engine run lean. Running lean will damage your engine.
    Having the tube hooked to the petcock is essentially plugging the tube (it pulls a diaphram in the petcock but does not let air in the tube).

    Lean refers to the air/fuel mixture having too much air.
     

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