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Help Vacuum - ZXR250A model in a C frame

Discussion in 'Kawasaki 250cc In-line 4's' started by Unkepttoenails, May 28, 2019.

  1. Unkepttoenails

    Unkepttoenails Demented

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    Ok so I'm still messing with my zxr and as some of you may know it has an A model in a C frame and I'm just wondering if I can take out the whole vaccum system as the carbs are jetted for the A and if I can what do I need to blank off or where too attach certain things do and what is the standard air/fuel mixture screw supposed to be set for on the A model engines . If anyone can help that would be greatly appreciated

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  2. crshbndct

    crshbndct Member

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    There is a complete service manual in the resources section, which should give you all the answers you need.

    What do you mean by take off the vacuum system? Both engines need a vacuum system. You wouldn't get fuel without it. There is a way to bypass the vacuum valve, but I've not done it so I wouldn't be able to help.
     
  3. Unkepttoenails

    Unkepttoenails Demented

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    The one in the resources is for a C model as far as I can see but I need one for an A for the specific engine if that's even a thing .

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  4. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    The bowl vents need to go back to the airbox and that's it. I normally use the "T" piece that's there to make a junction in between the vent tubes and then run that to the inlet at the top of the airbox ("A" in the second image) where the Vacuum Valve plumbing ends up on a "C" engine normally.

    You will also need to "end" the vacuum inlets on the boots of carbs 2 & 3. I just put a rubber stopper on them with a spring hose clamp.
    ZXR Bowl Vents.jpg
    ZXR Bowl Vents 2.jpg
     
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    Last edited: May 28, 2019
  5. Unkepttoenails

    Unkepttoenails Demented

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    @Frankster Thank you for the information and would you know if there is any benefit to this modification or simply less parts to go wrong ?
     
  6. Frankster

    Frankster See the World before you leave it Staff Member Premium Member Ride and Events Crew

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    Without being 100% certain, my understanding is that the vacuum valve is limiting the amount of air being vented into the bowls. It does this (again my assumption) by whatever vacuum is being generated from the carb boots on Cylinders 2 & 3 e.g. the faster the engine revs, the more air is lets into the carb bowls. I ran one for a while on a ZXR250A engine (with an A model TCI) and I didn't notice any difference to running without it. I've run ZXR250C motors without it and again no difference detected. I didn't check fuel economy, so maybe that's where it helps.

    I just make up a connector (like below) and get rid of all that extra plumbing.
    ZXR Bowl Vents 3.jpg
    Don't forget to close off the vacuum tubes in the boots of 2 & 3. Cheers
    ZXR Bowl Vents 4.jpg
     
  7. Unkepttoenails

    Unkepttoenails Demented

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    Sweet sounds like a plan to clear it up a bit thanks I'll do that so I think

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