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Thread: unusual mutations of airheadis motorcyclis found in the wild.

  1. #1
    Rally Rat
    Join Date
    Dec 2008
    San Antonio, Texas

    unusual mutations of airheadis motorcyclis found in the wild.

    So, I had to change out the carbs on my 77/7 r75.

    boy, did -that- turn out to be an adventure.

    See, the carbs were not spec for that bike, they were off of a 78 r100. Installation of a set of properly jetted carbs for a r75 resulted in the bike -immediately failing to run.

    Adjusting the carbs as richly as possible resulted in anemic operation of the motor, resulting in what looked suspiciously like fuel starvation when the throttle was opened.

    this resulted in closer inspection of the motor...revealing that the heads were not /7 heads, but /6 heads... curiouser..

    jetting the carbs all the way out to .175/.518(yes, I know, not a custom size), and adjusting the carbs to moderate richness resulted in pleasing performance, if somewhat poor fuel consumption.

    As near as we can figure, someone put an r90 top end and a .336 cam in this thing, -we think-. I've not had a chance to open it up and find out yet.

    it does -not- perform like a 750cc bike.

    however, it has a few limitations.

    I/met's running a /5 4 speed gearbox, and a 37:11 rear end. this results in it being 'quick' but not 'fast'. Also, horrible gas milage.

    Rummaging has produced an older 5 speed w/kicker, and a 33:11 rear end.

    I -think- this will wind up right around 75mph @4,000rpm, with fuel consumption right around 40mpg.


  2. #2
    The final drive ratio should vastly improve your fuel economy and top end. All airhead transmissions turn at a rate of 1 to 1 in high gear, so the transmission wouldn't change a thing. I am sending a PM about the 37:11 final drive.

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