Does anyone know the tuning specs for a Keihin carb VB 21B
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Thread: Does anyone know the tuning specs for a Keihin carb VB 21B

  1. #1
    Member lraklrak's Avatar
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    Does anyone know the tuning specs for a Keihin carb VB 21B

    Hello.
    I am am cleaning and trying to rebuild my Keihin carb model number VB 21B.
    I have a shop manual along with a Clymer manual.
    Neither manual has this carb model listed.
    Can I just use the tuning specs for a model 21A
    Please let me know.
    Thanks

  2. #2
    Senior Member Boomer343's Avatar
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  3. #3
    Member lraklrak's Avatar
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    Thanks.
    Now that I split the carbs apart that was another challenge.
    Did not realize that there are two areas that have to be on the spot.
    The picture with the blue arrow points to a spring that has to be hooked up the right-side throttle flapper.
    The picture with the purple arrow points to the throttle openings that have to be in sync.
    There are two washers.
    One goes underneath and the other on top.
    There is a spring but this presses on of the washer’s underneath
    Does anyone know the tuning specs for a Keihin carb VB 21B-1978-honda-hawk-ii-cb400-carb-1-copy.jpgDoes anyone know the tuning specs for a Keihin carb VB 21B-1978-honda-hawk-ii-cb400-carb-8-copy.jpg
    The carbs seem to work great mechanically.
    Next step is mounting the carbs and then a valve adjustment.
    I hope this will make this bike run almost like new.
    Like I stated in my other posts the bike has a compression of 153 psi in both cylinders (exactly) with 9,000 miles on it.
    It should be ok with these numbers.
    Last edited by lraklrak; 07-20-2019 at 06:54 PM.

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  5. #4
    Senior Member 80cb400t's Avatar
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    The reassembly of split carbs is a little finicky, don't forget about the spring that attaches the two choke flaps!
    As for vb21a vs. b it seems like the only difference between models is the mixture adjustment. I would start with 2 turns out and go from there.
    Carb synch once on the bike makes a pretty noticeable difference, although you might be pretty close with a bench sync.
    1980 CB400T - 1 running, 1 parts bike
    1965 CB160 - 1 kind of running, 1 parts bike

  6. #5
    Member lraklrak's Avatar
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    Yep got it together.
    The carb choke spring (blue arrow) is connected.
    Looks like they are in sync also.
    Just waiting to install it now.
    Also on the screws I had to use a high quality gun smithing screwdriver to tighten up those screws.
    That Craftsman screwdriver (in the picture) had no grip on the screws and would just slip.
    Does anyone know the tuning specs for a Keihin carb VB 21B-1978-honda-hawk-ii-cb400-carb-8-copy.jpg
    Last edited by lraklrak; 07-21-2019 at 12:36 PM.

  7. #6
    Super Moderator J-T's Avatar
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    Honda uses JIS screws, just a bit different than phillips.
    JT
    81 CM400T Under re-construction
    82 GL500

  8. #7
    Super Moderator longdistancerider's Avatar
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    You will need to at least check the sync of the carbs once it's running. I've only successfully bench sync'd carbs exactly 2 times, I was completely shocked when it happened.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 survivor restoration


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  9. #8
    Member lraklrak's Avatar
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    Got the carb (s) back on.
    It was a bit harder than I thought especially getting the boots all on.
    The cables were not that bad at all.
    Anyway, started the bike and now it responds much better to the throttle.
    No hesitation was so ever like before.
    Have not adjusted the piolet screws yet.
    I am glad this thing is running much better.
    Next for this is a cam chain adjustment and then the valves.
    After all that it goes on the road.

  10. #9
    Senior Member 80cb400t's Avatar
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    Once it goes on the road you might still have hesitation under load, don't get too concerned until the carb sync is done. I have learned that lesson myself.
    longdistancerider likes this.
    1980 CB400T - 1 running, 1 parts bike
    1965 CB160 - 1 kind of running, 1 parts bike

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