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cb750 k8 carb question

This is a discussion on cb750 k8 carb question within the Technical forums, part of the Caferacer.net Forums category; I have a 1978 cb 750 with the k8 carbs (that have the accelerator pump). I pulled them off over the fall and forgot what ...

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  1. #1
    Junior Member tsr4's Avatar
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    cb750 k8 carb question

    I have a 1978 cb 750 with the k8 carbs (that have the accelerator pump). I pulled them off over the fall and forgot what the extra tubing and inlet is for? take a look at carb number 2. I have connected in top picture the main fuel line, then to the left of it is a fuel line spot? or is it a blow off of some sort? The bottom picture shows them both hooked up... help a noob out!






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    Junior Member tsr4's Avatar
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    oh, yes I almost forgot... after looking at the clymer and the workshop manual, none of them seem to have this extra line going into #2 carb... just the fuel line from the fuel tank.
    \"thou art a boil, a plague sore\" W.S.

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    Senior Member Geeto67's Avatar
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    my first thought was that it was vacuum, esp since #2 is the carb with the accelerator pump. it isn't barbed so it doesn't look like it is meant to have a hose on it.
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    Senior Member catboy's Avatar
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    quote:Originally posted by Geeto67

    it isn't barbed so it doesn't look like it is meant to have a hose on it.
    +1
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    Senior Member oneworden's Avatar
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    I just looked up the carbs on babbittsonline.com and the hose that connects to it is called an air vent tube. Looks like a tube just slides on and runs down with the other draing hoses.
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    Senior Member Teazer's Avatar
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    I know this is an old thread, but isn't that the float bowl vent hose? It can be left open as long as there's no way water or dust is getting into the float bowl. I'd recommend fitting a hose .

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    Senior Member Teazer's Avatar
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    I know this is an old thread, but isn't that the float bowl vent hose? It can be left open as long as there's no way water or dust is getting into the float bowl. I'd recommend fitting a hose .

  9. #8
    Junior Member jaggedtimelapse's Avatar
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    Quote Originally Posted by Teazer View Post
    I know this is an old thread, but isn't that the float bowl vent hose? It can be left open as long as there's no way water or dust is getting into the float bowl.
    Is the above post true? I have a 78' cb750k and I recently took the gas tank off to clean the rust from the inside and now I'm not sure where or if this hose connects to anything. Although it is connected to the second carb like the OP photo. The smaller hose. the I'm a total noob so any help would be much appreciated. Can't find any other info about it. Seems like the manual doesn't specify either.

    I've attached a photo. Hopefully this is good enough to identify.

    If it is just a vent tube...can I just pull it through and route it underneath the seat next to the battery or something?

    Thanks in advance.

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  10. #9
    Senior Member Geeto67's Avatar
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    I am much less familar with the 78 carbs, but on the earlier ones they are between carb #2 and #3, yes they have two vent hoses attached that keep crap from coming in and clogging the vent.

    There is also a fuel tank vent that attaches to a plastic fitting and hose that runs near the battery box.

    it could be either of those.
    Ever tried. Ever failed. No matter. Try Again. Fail again. Fail better.
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    Junior Member jaggedtimelapse's Avatar
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    Thanks for your response!

    The plastic fuel hose that runs near the batter box Is still connected. In theory, it should be the one that I circled from the op's photo. If I'm not mistaken the other hose (not circled) connects to the petcock right? If it is THAT vent hose (circled), does it just route to the atmosphere and do you know the best place to run it?

    Thanks for your help man! it's much appreciated.

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