Guess Why?

Lets play little guess game with subject of Honda CB815 cafe-racer. Here is couple of photos to start.

Q: Why I draw some strange figures, mostly circles on 1mm graph paper?

A: I need to make electronic drawing of some part.

Sure, there is no need to guess why I make that 3D drawing. I need some part to be CNC machined from aluminum.

Q: What is this part for?

A: This part is a spacer that is to be put between clutch cover and engine case. That’s why part’s  outer shape meticulously repeats the contour of clutch cover.

Q: But really, why clutch cover needs be placed further than usually  from engine case?

A: Custom made clutch basket of new reinforced clutch protruding too far from engine case.

Q: Why do my Honda CB815 cafe-racer needs reinforced clutch?

This question I leave without answer for some time, but here is a small hint: the matter of this upgrade is related to what you may see on photo below…

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13 Comments

  1. Piotr

    What carb jet sizes did you use in your seven fifty?

    Reply
    1. gazzz (Post author)

      Hi Piotr,

      Sorry for late answer.

      Th main jets currently are 130. I also used slightly larger pilot jets, but I don’t remember of what exactly size.

      Kind regards,
      Nazar

      Reply
  2. Piotr Milcarz

    Thanks for your help Nazar. I will try to find somewhere which size od pilot jets should I use.
    Piotr

    Reply
  3. Robert

    Does the sven fifty exhaust header fits the CBX cilinder head? Thx!! Robert

    Reply
    1. gazzz (Post author)

      Hi Robert,

      Yes, headers are compatible, but there is difference. Both OEM header are of “pipe in pipe” type, see on this photo what i mean:

      https://www.gazzz-garage.com/wp-content/uploads/2016/11/IMG_7991.jpg

      Seven Fifty inner pipes are of smaller diameter than those of CBX.

      Yet one insignificant difference: exhaust studs of CBX750 is 8mm to 6mm while Seven Fifty studs are 8mm to 7mm.

      Reply
  4. Travis

    Awesome build!

    What were the final dyno numbers on HP and TQ?

    Thanks,
    Travis

    Reply
    1. gazzz (Post author)

      Hi Travis,

      We decided to keep this information unpublished until we’ll get a chance to participate in drag racing on some international cafe-racer event this year.

      Kine regards,
      Nazar

      Reply
      1. Travis

        Please keep me posted if you do that! What do you think it would run in the 1/4 mile? I have a 1992 Honda Nighthawk 750, my best pass was 12.73

        Reply
  5. Vivien

    Hello Nazar,

    Congratulations on all the hard work and sharing your experience!

    Your work inspired and motivated me to embark on a motorcycle renovation for the first time.
    I noticed you changed the clutch to strengthen it, which model did you install?

    Thank you
    Vivien

    Reply
    1. gazzz (Post author)

      Hello Vivien,

      Thank you for good words!

      It’s custom clutch. I made it using parts from thee different clutch baskets (some of them I modified) and custom made parts. So in fact it have no receipt.

      But there is no need in custom clutch as long as engine and it’s intake and exhaust are not heavy modified. Original CBX750 clutch with new spring and friction plates will do very well.

      Kind regards,
      Nazar

      Reply
      1. Vivien

        Do you think the CBX clutch supports the increased displacement?

        Reply
        1. gazzz (Post author)

          I assumed that you are about to only refresh engine. Even with permanence exhaust and re-jeted carburettors there will be no need in cardinal clutch reinforcement.

          Reply
          1. Vivien

            Thanks a lot for your answers.

            Kind regards.
            Vivien

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