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Thread: Fitting CV carbs from a motorcycle to a car.

  1. #1

    Fitting CV carbs from a motorcycle to a car.

    I was asked to do a thread about my 2t which has been converted to run on bike carburettors.
    I went this route for a few reasons.

    1. Im a motorcycle technition so this type of carbs are familiar to me.
    2. a set of webbers with manifold to bolt up are 1000 GBP+
    3. Cv carbs work well at any revs/throttle openings and help a cammy engine drive well at lower revs,also once set,dont need touching.
    4.they give about the best economy of all carbs when well set up.
    5. I had a set of NOS 40mm kehin carbs from a zzr100 which cost me 80.

    The downside was I needed to make a manifold to fit them up. Not such a bad thing.

    I dont have any pics of the process of building the manifold,but it goes like this....
    I took an inlet manifold gasket as a pattern,and cut this shape from 5mm thick steel,also blocking the water outlet from the head to the manifold.The bike carbs only need heating if being used in below zero deg C temps.
    I would have liked to use alloy,but i dont have access to a tig welder.
    Then I made a jig to locate the position of the throats of the carbs and shaped the runners from there,from 2mm thick stainless steel bends of 38mm dia.
    Silicone hose reducers join the carbs to the manifold. There is a take off on one of the runners for the brake booster. A electric fuel pump from a yamaha is ideal to supply the 3psi the carbs need. A mechanical one like the original on the car will cause flooding,as it will overcome the smaller floats. The electric bike ones can flow well at low pressure,and are pressure sensitive so shut off when the floats are full. You can blank off the fuel return.
    Then you need to fit up a throttle cable and choke cable.
    Obviously a 1600cc car engine(ive got the 2t)will pull a bit more air each stroke than a bike,so you will need to tune the fuelling. Many bike carbs have needles which can be raised or lowered to adjust midrange fuelling. The lower range/idle fuelling is done by the mixture screws,and full load is controlled by the main jet. Stock jets are usually in the 1.6 mm range. I took them to 2mm (which will probably be rich) and dyno from there.
    I used a ramair filter kit,which comes with a blank 1mm thick backing plate and you cut it to fit the type of carbs/bodies you have.
    I know they are not entirely period correct,but they just work.

    Here are the piccs i do have.

    Manifold with vac take off for brake booster.



    Test fitting



    Fitting air filter backing plate to remaining part of the bikes airbox. The trumpets remain inside the filter.



    And all fitted.


  2. #2
    Junior Member
    Join Date
    Apr 2012
    Location
    Portugal
    Posts
    23

    Re: Fitting CV carbs from a motorcycle to a car.

    nice job!
    it was a 2T-B engine? or single carb?

  3. #3
    Senior Member
    Join Date
    Feb 2011
    Location
    Bay Area, California
    Posts
    535

    Re: Fitting CV carbs from a motorcycle to a car.

    Terrific!

    Have you driven the car yet?

  4. #4
    Member
    Join Date
    Oct 2008
    Location
    Manila, Philippines
    Posts
    91

    Re: Fitting CV carbs from a motorcycle to a car.

    Cool! How does it run? No issues at all? I want to do this on my 4af engine

  5. #5

    Re: Fitting CV carbs from a motorcycle to a car.

    Yea it runs great. Id reccomend the conversion to anyone. It just takes a bit of care and knowledge of the carb tuning and there should be no probs. Like every thing its about the setting up.
    You need to install the carbs at the same angle they would be mounted on the bike,to get the floats shutting off correctly. You need a good manifold with no leaks,correct fuel pump and a dynojet kit or similar to tune them .Thats it.

  6. #6

    Re: Fitting CV carbs from a motorcycle to a car.

    Quote Originally Posted by CCoelhone
    nice job!
    it was a 2T-B engine? or single carb?
    It was a single carb. 5speed .

  7. #7

    Re: Fitting CV carbs from a motorcycle to a car.

    Not to sound like a certain British Top Gear presenter, but what would make more power? CV or DCOE carbs?

    POWAAAAAAAAAAHHHH, hehe.

  8. #8

    Re: Fitting CV carbs from a motorcycle to a car.

    Have done the same with my 2TC but running a set of 93 CBR900rr carbs with a Dynojet kit (Highly recomend made engine run way better!!!!). have been running this setup for about a year, made my manifold from a exhaust header off of a Dodge. Also made a manifold set for a 68 Datsun Roadster with a 2L he has a set of CBR1000 carbs on his with a Dynojet kit. The roadster has a big lobed cam, he was running side draft carbs that came stock on the car, very loppy and ran rough. after we put the set of motorcycle carbs drafted to the side, car ran 100% better idled like it came off of the factory floor purrrrrr.......

    thanks,

  9. #9

    Re: Fitting CV carbs from a motorcycle to a car.

    Quote Originally Posted by Gene
    Not to sound like a certain British Top Gear presenter, but what would make more power? CV or DCOE carbs?

    POWAAAAAAAAAAHHHH, hehe.



    Neither will make more power, assuming throat size is the same IE 40mm.
    The CV carbs benefit you by only opening dependent on engine demand, so you get no bogging down if you open the throttle too quickly. There is no accelerator pump to deal with.
    Being from a bike which has a cam to manage from 1000 rpm to 12000 rpm, means they work particularly well on a road car with a lumpy cam,adding driveability lower down.
    Yes you'll need to re-jet (or dynojet)

  10. #10

    Re: Fitting CV carbs from a motorcycle to a car.

    Ive had to tweak the carbs a bit,due to the engine being replaced,for one which flows significantly more air :lol:
    I didnt want to swap in a modern engine,I wanted to have a built 2t,to keep it true, Ill be keeping the original engine as well .

    I bought a donor 2tb.


    It had tar for oil,and a bent rod.



    No mind, block and head were good,which is all that counts. Got them chemically cleaned





    Kameri pistons,2tg, 89mm 11/1 comp.. (which one well known US supplier said wasnt suitable for a 2t :roll: )


    Billet fly. 3.1 kg :twisted:


    crower cam


    new timing gear


    Eagle rods




    Put a baffle in the sump.


    The head had some hours thrown at it to port it out and fit seats for 3mm oversize valves.





    All built up waiting to go in. Left it unpainted. Didnt want it over restored. Im not polishing every bolt all weekend,id rather drive it.



    Didnt take very long to swap it in. No fabbing needed.


    Tested it out :lol: :twisted: It made 135bhp and 135 torque at the wheels.


    I fitted a wideband to finalise the tune. Hope you like the noise

    https://www.youtube.com/watch?v=mZjH8MDtTQQ

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