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1980 Honda CB750F Cafe Build

This is a discussion on 1980 Honda CB750F Cafe Build within the Project Builds forums, part of the Caferacer.net Forums category; Originally Posted by tjurek51 First question for the group; I've seen inline 4 carbs swapped out for a 2 carb system, with aluminum intake manifolds, ...

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Thread: 1980 Honda CB750F Cafe Build

  1. #11
    Senior Member Teazer's Avatar
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    Quote Originally Posted by tjurek51 View Post
    First question for the group; I've seen inline 4 carbs swapped out for a 2 carb system, with aluminum intake manifolds, etc. what's the pro's and cons of this, from a performance and efficiency standpoint? better or worse than the inline 4 carbs?
    I believe that they come form Murray's Carbs and supposedly work very well on the street. Murray knows more about carbs than most and I suspect that the kit is better than most will achieve with pods and jets in OEM carbs. I would guess that CR carbs would make more power, but they were never designed to be used on a street bike. That doesn't mean they won't work, but like most things in life will be a compromise.

    That said, Mr Honda and his friends at Keihin managed to make modified OEM carbs work on the RCB endurance racers. The OEM carbs are not easy to get right, especially with an aftermarket exhaust without a lot of dyno time.

    Here's the link: https://murrayscarbs.com/product/cb7...i-carb-system/

    https://murrayscarbs.com/product/cb7...i-carb-system/

    For a full on Freddie Replica, CR crabs are the biz, but for the rest of us, maybe that's more than we need. Contact Murray and ask him.

  2. #12
    Senior Member CaTacL1sm's Avatar
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    Youd think Murray would use a less crusty bike to show off his product (referring to the first link). That picture makes it look like something someone cobbled together on DTT
    TrialsRider likes this.
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

  3. #13
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by CaTacL1sm View Post
    With a proper suspension and frame bracing, why wouldn't it perform on the track?
    It would perform scary fast if you couldn't also put track rubber on it. imho <- & for me the bike would still be too massive to comfortably throw around a track ymmv.


    ... it looks agricultural

    I thought he might have seen a pair of 2 barrel weber carbs on one :/ that's been done before too.
    Last edited by TrialsRider; 12-08-2018 at 12:44 PM.

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  5. #14
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by Teazer View Post
    ...
    That said, Mr Honda and his friends at Keihin managed to make modified OEM carbs work on the RCB endurance racers.....
    & Did they keep the air box or go with felt pod filters? lol

  6. #15
    jcw
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    Quote Originally Posted by CaTacL1sm View Post
    If you do it right, it will cost a lot, but it will be amazing



    Problem with building these old bikes is that you spend a lot of time and money, and some decent 17yo rider on a used craigslist 600 blows your doors off.

    At least they look way cool.
    Last edited by jcw; 12-08-2018 at 04:06 PM.

  7. #16
    Senior Member Teazer's Avatar
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    Quote Originally Posted by TrialsRider View Post
    & Did they keep the air box or go with felt pod filters? lol
    Neither. Open velocity stacks IIRC.

    Way back in the day the late Leon Moss of LEDAR who was a bit of a motor and carb expert, tried to get a CB900 to run with an aftermarket exhaust and he ended up with external tubes to equalize pressure in the carbs. I don't remember all the details but I think it went from rich to lean and back again as the throttle was opened.

    I have no idea if that was all one big pressure differential issue or an exhaust resonance pressure wave timing thing, I have no idea.

    That does raise a question as to how owners of cars with SU carbs (more or less the same design) get around those same flow/pressure wave issues.

  8. #17
    Senior Member CaTacL1sm's Avatar
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    Quote Originally Posted by jcw View Post



    Problem with building these old bikes is that you spend a lot of time and money, and some decent 17yo rider on a used craigslist 600 blows your doors off.

    At least they look way cool.
    True, but pouring money into an old deathtrap to make it slightly better can be so satisfying.
    jcw likes this.

  9. #18
    jcw
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    I'd love to know what framecrafters did for this chassis.
    Tires are clowny. But suspension looks top notch.
    I'd ride the shit out of it...

    Framecrafters Project Showcase - Bikes and Frames


    I would brace the frame (doesn't have to complicated, some well placed proven ones), then figure out how to fit modern rubber in decent sizes to the front and back. 110, 120 front, 150-170 rear. That likely means a fork swap but not necessarily USD. That way you get bigger rubber up front and better brakes, too. Set the geomtery, brace the swingarm and space for the larger rear wheel. Quality bushing for the swingarm, bearings for the steering head.
    Update the fork internals if possible, upgrade to nice rear twin suspenders.

    Ride it for a while until you get bored of the stock power, spend more money on engine mods. Those are pretty well sorted...
    Last edited by jcw; 12-08-2018 at 04:41 PM.

  10. #19
    Senior Member tjurek51's Avatar
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    Trials, I'd have to say no, my current carbs do not give me nice even throttle. idle to mid is a bit of a sputter. WOT gets me to about 90 mph tops and seems solid. though I had one time when suddenly had loss of power going freeway speeds. pulled over, shut it down, waited a minute, restarted it and it's run fine ever since. I've not touched the carbs since I bought it, other than keeping clean, high proof petrol in it and stabilizer in storage.

    i'm definitely moving to the flat side CR carbs for the rebuild. want to move to pods and the CVs are shit for that, from my experience. tried it on the 900 project and couldn't get it tuned. I've not worked with the CRs but my understanding is they're better designed for PODs.

    but appreciate the thoughts. will stick to the 4 carb set up. I've seen the aluminum billet intake manifolds for the CB750. are they worth it or should I stick to rubber?

  11. #20
    Senior Member tjurek51's Avatar
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    couple of chicken scratch ideas. First Conceptual look;
    Name:  Conceptual Drawing 20181214.jpg
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