Jetting Guru's! Dual 3 jet Keihin CDK2 40's help! - Page 2
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  1. #11
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Quote Originally Posted by hooka-2 View Post
    I ran a set of those 3 jet Keihins for a while with a mild 750. I raised the middle jet one size because of the aftermarket flame arrestors. Other than that I used the stock jets and just opened the needles a little.
    This may be the exact thing I'm missing. I'm going to try this to cure a mid range hesitation. Did it have a mid range weirdness prior to the change? I'm running factory pipe's jetting, which is supposedly set for aftermarket flame arrestors but idk its not perfect yet. I've been trying to change the low jet around but that's not solving the problem. I think its after that.
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake, PWR ride plate [47.3mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, Coffmans Sizzler [49.1mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1995 SJ MINT:
    Worx 205 intake [42.5mph gps]



  2. #12
    PWCToday Newbie ttytwstr19's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    My pop off ended up being too high. I guess I took for granted how important setting this the proper way was when I rebuild the carbs. I lowered that along with one size bigger one the bottom, on size bigger on the top, and she rips. I couldn't be happier! Good luck!

    Jon

  3. #13
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Thanks for the info Jon. Did you cut the springs or find shorter ones to lower the pop off? So you're at about 75 45 138 or 140 now? I've got two sets of these carbs so I'm going to set them up a little different and see what happens.
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake, PWR ride plate [47.3mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, Coffmans Sizzler [49.1mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1995 SJ MINT:
    Worx 205 intake [42.5mph gps]



  4. #14
    PWCToday Newbie ttytwstr19's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    I used the shortest of the three that came with my rebuild kits. My jetting is now 138 /72 /48. About 1.5 out on mixture screws. Also, dont overlook your idle setting. as trivial as it sounds, if the idle is too low, itll trip up a bit when it goes from the idle curcuit to mid - Hope this helps!

  5. #15
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Got it, I should have those extra springs also from my rebuild kits. I'll give that a try on one set, and try upping the mid jet on the other. I'll report back with my findings. Its good to have one thread where we keep this info for these 3 jet carbs.
    1985 JS550/800 "Pretty Red": Newmiller 800, Rhaas 750 pump conv. [56.3mph gps]
    2009 1100 SJ:
    Kawi 1100 build in progress
    2009 SJ MINT:
    KP steering adaptor, Worx 228 intake, PWR ride plate [47.3mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, Coffmans Sizzler [49.1mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1995 SJ MINT:
    Worx 205 intake [42.5mph gps]



  6. #16
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Quote Originally Posted by ttytwstr19 View Post
    My pop off ended up being too high.

    Jon
    There is no such thing as a pop-off that is too high! When dealing with Keihin carbs, you need to know where the
    vacuum leaks are. Hi pop-off pressure is a balance between the jetting and the spring rate, when all vacuum leaks
    have been eliminated.

    High spring rates is an opportunity to make much more low end power than a low pop-off.

    Just in case, all Keihin jet #'s represent their diameter in mm's (130 = 1.3mm diameter)
    Last edited by wmazz; 08-02-2013 at 05:33 PM.
    Horsepower == Speed, RPM != Speed



  7. #17
    PWCToday Newbie ttytwstr19's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Quote Originally Posted by wmazz View Post
    There is no such thing as a pop-off that is too high! When dealing with Keihin carbs, you need to know where the
    vacuum leaks are.
    Gotcha! Ok, well, I lowered my pop off to 32 psi and it fixed my problem - or at least it is happy. Either way, I couldn't be happier with how my ski is running.

  8. #18
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Quote Originally Posted by ttytwstr19 View Post
    Gotcha! Ok, well, I lowered my pop off to 32 psi and it fixed my problem - or at least it is happy. Either way, I couldn't be happier with how my ski is running.
    That's Great, but the problem that caused you to lower your pop-off still exists. Lowering pop-off pressure is just a band-aid at best.
    Horsepower == Speed, RPM != Speed



  9. #19
    PWCToday Newbie ttytwstr19's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Quote Originally Posted by wmazz View Post
    That's Great, but the problem that caused you to lower your pop-off still exists. Lowering pop-off pressure is just a band-aid at best.
    So what's the magic pop off number I need to chase? The carbs were apart when I bought the ski. I have no idea what it was stock. I only know that from when I rebuilt them using a stiff spring , the ski ran like crap. It was so stiff, my 40 psi guage was at its limits. I lowered it to what it is currently and it's better. Where should I be looking for for problems? I've been through everything and I'm pretty confident everything is the way it should be.

  10. #20
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Sorry, I see pop-off pressure used by mechanics as some magic pill, so they don't have to fix, or diagnose their customers real
    problems. I also didn't notice this was an old thread.

    There is no magic pop-off #. But the stock pop-off works fine, except for when there is a problem.

    When you lowered the pop-off, you richened the low speed jet by several sizes, and the overall amount of fuel was increased.

    The low speed jet, the pilot fuel-air screw, and the spring rate are all balanced. Over time a vacuum leak under the carb throws
    that balance off. Many mechanics will just lower the pop-off, and send the customer down the road without fixing the vacuum leak.
    The magic pill works, and everybody is happy.

    When I jet, I strive to get a baseline of 3/4 pilot and main. So if anything changes my screw settings, I know there is a reason for it.
    Everything on watercraft happen for a reason. Being able to recognizing a symptom of a problem is whats important.

    From what you have said, your engine still wants more fuel. At least a couple more jet sizes on the mains, and possibly on the low.
    But "Being able to recognizing a symptom of a problem is whats important." Why does your engine still want more fuel? It depends
    on your engine rpm. If it is lower than 7000rpm, the engine needs more fuel because it is working harder than it should. That is
    what happens when the pump doesn't allow the engine to make peak HP. If it is producing 7000rpm, then it is simple, the engine
    just wants more fuel.

    That pipe made peak hp at 6750rpm on a perfect JS650. But with the extra exhaust timing your cylinder has, the math is very close
    to 7000 rpm. (I know I said 650, the 650 pipe was modified to wrap around in 93', but they are the same pipe.)

    Have you already completed any WOT runs?

    If you want some guidelines on fine tuning your ski, keep this thread going. Otherwise I am sorry I butted in.

    Sincerely


    Bill M.
    Last edited by wmazz; 08-03-2013 at 04:10 AM.
    Horsepower == Speed, RPM != Speed



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