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The Majestic Motobi 125

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  • griff851
    Moderator
    • Jun 2007
    • 3824

    The Majestic Motobi 125

    With hysterical race season about to begin, I thought this year I’d surprise Pete and get all three of his race machines up. At Stanthorpe at the beginning of March we had a test and tune. 5 sessions a day, 10min each. Fast, Intermediate and slow. CBR250 in Fast, 250 narrow case in intermediate and Motobi in slow. The cbr’s first outing after Pete binned it at Morgan park, the 250 NC just doing more track time, and the motobi was just supposed to get around the track and see what happens.
    poor little Motobi was an ex methanol from 20 years ago. It had a shot rocker pin bush and valve guides, and no carby. Pete supplied some boxes, a frame and set of forks and a couple of wheels. And said can you make this a race bike please. That was 5 years ago.

    After a procrastination period of a couple of years, I peered into the boxes and like Neil Armstrong I got on with the job.
    Of coarse nothing just fitted together. All of it in the end.
    Head came together and got fitted up nicely. Then the fun bits. Find and replace serviced front forks for correct items. Find triple clamps that actually belonged. Make and replace lower triple clamp spindle. Weld on steering stops, replace front hub………….. manufacture:- tank and seat mounts, rear set mounts, rear brake cables and linkages lever attachment and mount, gear lever linkage, front brake cable, brake stay, cable adjuster assembly and mount, tapered head fork caps, wheel spacers internal and external, steering head bearing cups, coil mount and fairing brackets. Complete exh system.

    So after finally after doing stuff, carby time. Pete likes period look so I sent him on a mission SSI 26 remote bowl and we’re in business. Pete turns up with a box sometime later. Nice. “Were are the jetty fitty bits and gubens? Brought it incomplete cheap. I price up the bits $2000. Mmmm. I’ll make bits later. $50 VM22 pit bike is going to have to do.

    Big problem. 31mm wide 27 mm high “port job” in 7mm. inlet manifold 31mm id with wrong angle for vm22. Oh well, just have to around the track. It did. Badly, very badly. 5 times. Pete will try and ride anything that runs. This attitude towards things has resulted as expected when a mate did his el cheap arse prep. 4 crashes and multiple strandings all down to machine issues. He’s keen, I’ll give him that.
    I retired it at the test and tune, to painful to what man vs machine any longer. Test part of test and tune over.
    the 250 NC blew a base gasket after 7 sessions.

    The first week was spent machining a blank 56T rear sprocket for CBR so it looks like original fit and a re jet and tune, as well as a barrel base gasket and gearing change on the 250NC

    So for the last 2 weeks it’s been getting the inlet runner solution sorted. I threw a piece of 6065 at the lathe and it turfed back a thin tapered 25.5mm spigot ring that I pressed and glued into the inlet port. It was just springy enough to distort giving a not to bad port shape in the end.
    found a bit of 90 stainless 26 x 1mm tube, whipped up some flanges, got magic Manny the welder to stick it together. A bit of jetting and spark plug tomfoolery and ta dah, today I’ve got a runner. Spins to 9k by the sound of it, pulls clean and perfect plug burn. Surprisingly quick and powerful little devil. Tap it on in First, snap into second and you can feel the front lifting.
    Pete’s in for a surprise!

    Track ready for round 1 of 5 this year.
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    Last edited by griff851; 03-25-2023, 10:08 AM.
    Griff
    To infinity and.......
  • griff851
    Moderator
    • Jun 2007
    • 3824

    #2
    You do not have permission to view this gallery.
    This gallery has 4 photos.
    Griff
    To infinity and.......

    Comment

    • griff851
      Moderator
      • Jun 2007
      • 3824

      #3
      1962 if anyone is interested
      Griff
      To infinity and.......

      Comment

      • marvin
        Administrator
        • Apr 2007
        • 2949

        #4
        Good one Griff !!

        Comment

        • griff851
          Moderator
          • Jun 2007
          • 3824

          #5
          Thanks Marvin. Means a lot, 2 weeks and it’s time to win races. Not quite sure how I feel about it being the only one it’s class. Still if it gave the 150’s and 175’s a tickle up, highly unlikely, but way cool if it could. We’ll see. It seems to be on song or very close.
          I got a guy to sit in the seat for the 888, A grader TT and stuff, he’s been a mate for 37 years. I said Brett, want to ride the 888? Of coarse was the reply. But.. I said, there’s an issue. You would simple just win. No RC 30’s, nothing, except maybe the odd Katana if you were lucky. And, cycles to failure. Which means you have to chose your battles wisely. He’s ridden it before out on some seriously fast asphalt country. Still in philosophical discussions.
          Griff
          To infinity and.......

          Comment

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