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  1. #1
    CB750 Member chuckt's Avatar
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    Breather at front of engine?

    Can someone tell me what the hose at the front of my 1993 cb750 engine is? I bought the engine from eBay, and there is a cut hose right by the oil cooler lines. I am assuming (correct me if I am wrong) that the two that I have on the rear side of the engine I can T together and route at the bottom of the bike, but then I found this other one, so I am wondering if it is another breather tube.

  2. #2
    CB750 Member chuckt's Avatar
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    OK - I found what this is on BikeBandit. It is titled "Pipe, Air Pass", part # 12115-MJ1-790. Obviously a hose hooks on it, but does it go anywhere?

  3. #3
    CB750 Guru amc49's Avatar
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    Not a breather, rather a check valve. A hose pulls filtered air from airbox to that check to then pass it up into the exhaust to afterburn for emissions. Part of the passive pulse air injection that bike has. The point there has limited low vacuum and slight exhaust pressure if the check is not working, you can block it off too but consider how close to big heat you are when you decide how to do it. Rubber hose may melt if close enough or the check leaking to backflow exhaust.

  4. #4
    CB750 Member chuckt's Avatar
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    Ok - it has a short piece of bląck hose on it now. I guess I could put a brass fitting in there and clamp it in...

  5. #5
    CB750 Guru amc49's Avatar
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    Block it off. The flow there is metered by a valve by airbox but with the valve gone and open tube then pulling big air by pulsing will cause afterburning (backfire) in pipe.

  6. #6
    CB750 Member chuckt's Avatar
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    Now that makes sense. I love as at Honda the other day picking up some spark plugs and we were discussing the build. They had no idea what it was for.

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