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  1. #11
    PWCToday.com Is My Home Away From Home
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    Re: 650sx Sudco 42 jetting?

    Revving her up on the stand she seems to have a mid range rich bog. Thinking I might need a new needle and possible and stiffer spring. Anyone know where I can buy jets and needle/springs for kehin carbs?
    triceps are the biceps of the back of your arm.

  2. #12
    Attention ***** PWCToday.com Is My Home Away From Home JonnyX2's Avatar
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    Re: 650sx Sudco 42 jetting?

    DO NOT throw away the original spring, save it for later. I have seen so many Keihin rebuilds that got jacked up using a/m springs. You will thank me later
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  3. #13
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 650sx Sudco 42 jetting?

    Quote Originally Posted by wmazz View Post
    In the past I have seen 650 specs 75/145.
    Quinc, these specs have been bothering me. I have found another Sudco 42
    with leaner specs than this, but it still bothers me because I don't think these
    carbs are special, or more capable of running great on leaner specs than any normal
    carb.

    For example, the single Keihin for a 750 ss runs a 75/155 and that carb has
    a main jet booster (bomb sight).


    I believe that jetting near 75/175 would work better (because the 42 has no main
    jet booster), with ~24 psi pop-off. I would also try to aim for 3/4 turns out on the
    low (pilot) screw, but if you need more turns, try increasing the low jet size. On the
    high speed screw, start rich (1 1/2) and tune from there.

    It may be possible to run in 80 low, with a higher pop-off ~30psi.


    Bill M.
    Last edited by wmazz; 05-27-2019 at 04:55 PM.
    Horsepower == Speed, RPM != Speed



  4. #14
    PWCToday.com Is My Home Away From Home
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    Re: 650sx Sudco 42 jetting?

    Quote Originally Posted by wmazz View Post
    Quinc, these specs have been bothering me. I have found another Sudco 42
    with leaner specs than this, but it still bothers me because I don't think these
    carbs are special, or more capable of running great on leaner specs than any normal
    carb.

    For example, the single Keihin for a 750 ss runs a 75/155 and that carb has
    a main jet booster (bomb sight).


    I believe that jetting near 75/175 would work better (because the 42 has no main
    jet booster), with ~24 psi pop-off. I would also try to aim for 3/4 turns out on the
    low (pilot) screw, but if you need more turns, try increasing the low jet size. On the
    high speed screw, start rich (1 1/2) and tune from there.

    It may be possible to run in 80 low, with a higher pop-off ~30psi.


    Bill M.
    I am willing to try that working my way down in jetting. I just haven't figured out where to get jets yet. Reading some more the stock 38mm keihin on a 650x2 came with 75/140. Being 4mm bigger and having a pjs pipe the jetting I have now doesn't seem that high? 82/152.
    triceps are the biceps of the back of your arm.

  5. #15
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 650sx Sudco 42 jetting?

    Here is a comparison of similar carb diameters for a similar engine size.

    650 => 38 cdk2 jet total 75/140 = 215
    587 => 38 SBN-i jet total 210 ---------- Very small main jet booster
    650 => 42 sudco 75/145 = 220 ------- No main jet booster
    650 => 42 sudco 82/152 = 234 ------- No main jet booster
    650 => 44 SBN jet totals 240 to 260
    650 => 42 sudco 75/175 = 250 ------- No main jet booster
    720 => 40 SBN-i 67.5/175 = 242.5 ---------- small main jet booster w/ accel pump.


    Bill M.

    720, shorter stroke, larger pistons
    Last edited by wmazz; 05-28-2019 at 02:30 AM.
    Horsepower == Speed, RPM != Speed



  6. #16
    Resident Guru RenoJetTech's Avatar
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    Re: 650sx Sudco 42 jetting?

    Quote Originally Posted by Quinc View Post
    Revving her up on the stand she seems to have a mid range rich bog. Thinking I might need a new needle and possible and stiffer spring. Anyone know where I can buy jets and needle/springs for kehin carbs?
    A few on interweb.
    '88 550-ride plate,intake grate,intake manfold,carb
    '96 GTX-1mm overbore,F/a's,intake grate,port timed for mid and top end
    '95 FX 1- usually take this motor to 753cc with exhaust porting and reeds

  7. #17
    Resident Guru RenoJetTech's Avatar
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    Re: 650sx Sudco 42 jetting?

    I'll be tuning a similar but a little different 650sx. Biggest difference ? BN44, 40mm venturi
    '88 550-ride plate,intake grate,intake manfold,carb
    '96 GTX-1mm overbore,F/a's,intake grate,port timed for mid and top end
    '95 FX 1- usually take this motor to 753cc with exhaust porting and reeds

  8. #18
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    Re: 650sx Sudco 42 jetting?

    Atlantic Jet Sports sells Keihin jets and rebuild kits. I believe you can purchase OE Keihin needle/seat and springs as well.
    Last edited by candysucker; 05-28-2019 at 10:02 PM.

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