Tuning Keihin CV Carbs 72 CB350
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Thread: Tuning Keihin CV Carbs 72 CB350

  1. #1
    Member Alewiska's Avatar
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    Jul 2018

    Tuning Keihin CV Carbs 72 CB350

    I’m trying to vacuum balance the carbs on my bike. I have two questions regarding the stock carbs on the bike.

    1) Would vacuum tuning require a modification to the boot for a vacuum port? If so is there a technique recommended or a link to a good video?

    2) Does anyone know where to get a spare brass pressfit fuel intake? It looks like mine popped off somewhere during the rebuild.

    I'm attaching pics of the carbs. I can't find the diagram for these anywhere so I'm not sure if the large press nipple towards the back of the carb is the fuel inlet. If so I'm ok there, but, there is a nipple missing on right carb that is the small brass nipple on the left carb.

    Tuning Keihin CV Carbs 72 CB350-right-carb.jpg

    Tuning Keihin CV Carbs 72 CB350-left-carb.jpg
    Last edited by Alewiska; 05-21-2019 at 08:45 PM.

  2. #2
    Sensei 66Sprint's Avatar
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    Sep 2008
    Roanoke, Virginia
    The #2's are the overflow tubes and you should be fine as is....
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  3. #3
    Member jjdugen's Avatar
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    Dec 2018
    You can use syringe needles through the rubber of the carb manifold. This does involve a puncture in the inlet rubber but the hole is so small it self heals. It is not a technique I favour but sometimes needs must. These carbs are not particularly hard to balance by ear and feel, the exhaust gas pressures are a pretty good guide.

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  5. #4
    Supporting Member Yendor's Avatar
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    Aug 2011
    Camden County, New Jersey - USA
    As said the missing tube is for the Overflow.
    If it was me I would take the Carb Bowl with you to a hobby shop where they sell misc brass tubing and find a size that is a press fit and cut to lenght.
    All it does is route any fuel dump from a stuck float or ? to a place where the engine won't catch on fire.
    There is a small bracket LOOP that the rubber tubing goes into to dump it out down by the rear wheel.
    Simple fix.

    As far as the vacum tuning its really not required.
    As said before too - they are easy to balance by ear and exhaust pressure.
    1970 CB 350 CAFE - Current Project on the bench,
    1972 CB 350 K4 Red - Now a Happy Rider ! !
    1972 CB 350 K4 Green (My Sons) DONE - YES !,
    1st Bike 1970 SL 350 (Brought home in Parts - Trailer/Trunk/Back Seat - I miss that bike),
    2nd - Bike Kawasaki 750
    3rd - '73 XLCH 1000

  6. #5
    Senior Member Erwin's Avatar
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    Aug 2013
    You can add a vacuuum port. For instance, Dime City Cycle sells 5mm brass tubes that you can fit to your head or intake rubbers. Most people fit them to the head and not the intake rubbers. I have not seen a lot of people doing this modification to their CB350k's. Like mentioned above, most people find it good enough to do it by ear and feel. I can imagine that you want to do this modification if you are a perfectionist and especially finicky about details... like myself.

    Last edited by Erwin; 06-03-2019 at 02:34 AM.
    1972 CB350K3 General Export | 1976 CB200T K0

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