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Thread: 250 race bike

  1. #1
    Join Date
    Jun 2007
    Bris Vegas

    Default 250 race bike

    Well ladies and gents, after 25 hrs pissing around with the 1962 250 Ti valves narrowcase, I finally got it going. It's using a Dellorto SS1 35 B with a 13.5mm lift factory cam I came across. I also did some inlet port work. An interesting experiment with modifying a straight shot port using a theory I had, and velocity porting. My idea is to increase swirl through the shape. A bit radical and I've used it on my yet to be started twin. A bit ugly in the pic by it will clean up nicely. Original port is second pic for comparison. The best bit is, it's only a 32.5mm inlet, proof bigger isn't necessarily better, and if you do the maths you get a result.
    So I bit the bullet and stuck the bike on the dyno Monday night. My god. I didn't get power figures because most of the session was spent just getting it to run. Power comes on at 10500 and I didn't go past 13800. The rearset is just a blurry gray thing at those revs. I've had it to 12500, but this time it had a more solid drive feel to it, ie way more torque. Swirl theory component in action.
    Unfortunately I have an issue between 4000 to 10500, fueling air flow I believe is due to the 15mm cutaway on the slide. Getting a new slide shortly. It's behaving just like a clogged fuel filter, you have to joggle the throttle to keep it revving with no power, so a major struggle getting into the power band. But once it comes on song, bloody hell. The noise was amazing and I got a full body buzz and even let out a ya- f***ing-who! Bevan was certainly impressed and confirmed I may have an insanity problem.
    Last edited by griff851; 09-20-2017 at 12:25 AM. Reason: Pics removed. Possible patent issue
    To infinity and.......

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