Drill Bit Size vs. Carb. Jet Size


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Thread: Drill Bit Size vs. Carb. Jet Size

  1. #1
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    Drill Bit Size vs. Carb. Jet Size

    How do you calculate Keihin jet size? I want to drill my extra #210 Factory Pro jet to a #230 or #245.

    I found this conversion, and wondered if somebody could verify it..
    Kiehn jets are represented in percentage of a MM. A low speed jet thats marked 42 would be 42% of 1 MM (.03937) or .0165.

    That means (approx.):
    #225 = .08858 which is a size #43 drill bit
    #237 = .0933 which is a size #42 drill bit
    #245 = .0964 which is a size #41 drill bit

    Can anybody verify? Thanks!

  2. #2
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    Send a note to CharlieD. He has done the drill bit thing before.

  3. #3
    Charlie D's Avatar
    Charlie D is offline Senior Member
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    take the size jet you want and divide by .0394 (.03937 = 1 mm)

    I have never known anyone that has been able to get any more out of a 1300 with a jet over 225 in size.

    Best top end with a wide open filter is with around a 220 and the use of a 60 pilot

  4. #4
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    I am running a open element, 215 main drilled from the stock. Pulls hard, runs real clean.


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