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Discussion ZXR250C Vacuum Valve Purpose?

Discussion in 'Kawasaki 250cc In-line 4's' started by StarletRick, Sep 12, 2017.

  1. StarletRick

    StarletRick Active Member

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    I have a question that I’ve tried searching for a definitive answer, and can’t find one..

    The vacuum valve thing up by the headstock – what exactly does it do? I'm assuming some kind of prehistoric emissions doodad.. I can’t see any reason to keep it but thought I’d ask here first. I've never seen anything quite like this on a bike, but my bikes are either way way older or a lot newer... must have been a 90s thing!

    From that I can gather, the 250A doesn’t have it, so does anyone have the plumbing diagram for that engine so I can remove it?

    Thanks,

    Rick.
     
    StarletRick, Sep 12, 2017
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  2. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    From a post @sharky made in my ZXR thread

     
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    Linkin, Sep 12, 2017
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  3. StarletRick

    StarletRick Active Member

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    why would i run the vac lines to the airbox? wouldnt i just block them off?
     
    StarletRick, Sep 12, 2017
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  4. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    That is how the A models have their lines run according to sharky. I don't have an A model so I wouldn't know.

    The petcock is vacuum operated on both A and C models so that may be why
     
    Linkin, Sep 12, 2017
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  5. StarletRick

    StarletRick Active Member

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    Yeah, 1+4 operate the fuel tap, 2+3 go up to the vac valve and the 2 carb vents on the top also run to the valve. Which then runs to atmo and the top of the air box.

    My plan was to leave 1+4 alone, block 2+3, and run the carb vents straight into the air box - this would then let me pull the vacuum valve thing.

    I’m just struggling to see what that valve actually does? Just seems completely unnecessary, but I don’t want to remove it if for whatever reason it does something I don’t know about and causes me issues. again, my experience with working on carbs is from my '60 Triumph, which is about as simple as it gets. its a good learning curve!

    Rick.
     
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    StarletRick, Sep 12, 2017
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  6. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    It might be an emissions doodad. It could allow fresh air in one way and not let any fuel vapours out the other.

    Modern vehicles have to have fully sealed fuel tanks - no venting to atmosphere.

    There are a few ways to achieve that, like a charcoal cannister on old cars. BMW must have thought it was a good (or cheap) idea, since their new G310R learner bikes have them.
     
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    Linkin, Sep 12, 2017
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  7. sharky

    sharky Well-Known Member

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    @Linkin sorry,I should have checked my post better that day I left a few key words out -- BLOCK hoses 2+3, CARBS to airbox :oops:, that was actually a mates balius I was going off back then I had never had an A model until recently which I have hardly had a chance to look over yet, will do tomo. Hi @StarletRick you were absolutely correct with the vacuum hose plan, I don't know what the vacuum valve does either, there would be less emissions though recycling back through the airbox wouldn't there, the hose to the open air is the difference.
     
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    sharky, Sep 13, 2017
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  8. Adam Giles

    Adam Giles Well-Known Member

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    On my a model, vacuum on 2+3 were connected to each other. Vacuum on 1+4 are linked and connected to petcock. Balance pipes on top of carbs run to airbox. I copied this onto my c model and all works fine.

    Sent from my SM-G920F using Tapatalk
     
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    Adam Giles, Sep 14, 2017
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