Jetting Guru's! Dual 3 jet Keihin CDK2 40's help! - Page 3
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  1. #21
    PWCToday Newbie ttytwstr19's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Bill,

    No apologies needed. I'm not an expert, just an enthusiast. I have been out of standups for 20 years and this 96' 750 was my intro back into the sport. If someone has knowledge to share, I welcome the opurtunately to learn!

    The only thing I guess I don't or didn't know was where I should be for pressure. If stock pop off was 30psi, then I guess 35 psi is good. If its 60 psi, then yeah, I'd say I have left a lot on the table and I need to be looking for some problems. I've ridden the ski, it seems to go great. I don't have much to compare it to as I said before, I bought this as a basket case, built it, never rode it stock (or any stock 750, my last ski I own was a 89' 650 back in 89!) , so I have no seat of the pants experience on this specific ski. I can compare it to my buddies stock 800 SXR, my ski pulls harder and is waayyy faster. As far as wide open runs, yeah, I've ridden the hell out of this thing, done good 30 second WOT plug chops, they seem to be decent. I run a 40:1 premix castor 927 oil and super, so plug readings can be a bit misleading, I've always run my 2stokes a tad on the rich side, but I don't blow up motors.
    What do you run for the data acquisition? Other than a mini tach, how can I verify I'm actually getting full Rpm?

    Great info.

    Jon

  2. #22
    PWCToday.com Is My Home Away From Home Chris03HD's Avatar
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    Bill M, please keep typing!

  3. #23
    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!

    Bill thanks for the info, and what rpm that pipe makes peak power. Its clear I need to drop my RPM some on my 550/750. One question. All else equal, how would you adjust for aftermarket flame arrestors on an otherwise stock engine with no leaks? Or perhaps an engine with just a pipe and aftermarket flame arrestors? It has been my experience that you need to lower pop off with a/m f/as to compensate for the lower vacuum. Also given your experience with PJS and the 650 pipe, do you have any jetting guidelines? Most 650 pipes you simply adjust the high screw open a bit for example.

    Back to the subject of the 3 jet dual Keihins, I put together two sets of carbs this weekend. The first set was stock ss xi 3 jet settings, with a 50 mid jet instead of 45. Jetting is 72 50 135 with stock & seat and middle length stock springs. Low screw out the stock amount of 1 1/8 and high 1. I can not tell you how much the 50 mid jet improved things. Overall the low to mid throttle response was MASSIVELY improved. Right off idle it is perfectly responsive. It is a totally different ski.

    This engine is my only one I haven't rebuilt. I'm not sure how air tight it is. It has run great before though and had its crank seals replaced at least once prior to my purchasing it. Because I'm running way less restrictive Tau Cetis it made sense to me to drop the pop off. Since I only had one set of shorter springs, which were in use, I decided to up the mid jet to compensate. Boy did it work.

    I also noticed that my xir carbs, which stock have 68 45 130 jetting, had shorter springs and the same n & s. I'm guessing that's how they got away with the smaller pilot jet. It probably just worked better with the PJS pipe. Although, I need to confirm those shorter springs were in fact stock to the xir. I'll get back on that. Just seems to make sense. Anyway my second set of carbs was set up to xir stock, with the lower pop off. At some point I'll test this set.

    But really, I know several of us have a weird mid range hesitation with these carbs. Upping the mid jet helped in my case. So well in fact that I'm not going to swap the carbs out for my sxi pro Mikunis.

    Also one last thing, one of these days, probably in the off season, I'll test the pop off. At the moment, gut seat of the pants tuning is working pretty well. This past weekend I didn't have time to test given limited riding and wrenching time.

    But yea, if you guys have 3 jet Keihins with a weird hesitation keep this in the back of your mind. Mid spring length (stock) and just up on the mid jet to 50. Massive improvement.
    Last edited by theVetteman3; 08-04-2013 at 06:39 PM.
    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 [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



  4. #24
    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!

    I will get back to this thread this evening and answer ttytwstr19 questions.


    Quote Originally Posted by theVetteman3 View Post

    But really, I know several of us have a weird mid range hesitation with these carbs. Upping the mid jet helped in my case.

    I wanted to mention that Keihin sold the 3 jet carbs as a product to Kawasaki. Keihin engineers did the same with PJS, but I
    don't remember if they were 2 or 3 jet carbs. Next the manufacture gives the carbs to the manufacture to test and develop
    their own jet specs. That is exactly what Kawasaki did, but they didn't do a good job of it. They accepted Keihin's low speed
    bypass holes (at the throttle butterfly) as ok, or not requiring any change. Instead Kawasaki R&D just tried to increase the jet
    sizes to overcome bypass holes that were too small!

    I have also noticed "the weird mid range hesitation with these carbs," and a it helps to modify the upper bypass holes, but
    the bottom 2 must be left alone.

    I still remember the specs, but I hesitate to post them because the vacuum leaks on the bottom, and front of the carbs are
    so important that they should be repaired first.

    This quote is from another post, and explains the different types of pilot circuits

    Quote Originally Posted by wmazz View Post

    Just for information: there are 3 types of low speed screws:
    (i) (38mm round body Mikuni) simple low speed screw that provides fuel to the low speed bypass
    holes (at the throttle butterfly), and controls the starting and low speed response.

    (ii) 44mm round body Mikuni) Pilot fuel screw has a fuel source separate of the low speed screw.
    It only meters fuel (sounds normal), and uses a low speed screw in conjunction with the pilot screw.

    (iii) (Super BN & Keihin carbs) Pilot fuel air circuit. The fuel source of this circuit is the low speed jet,
    and is different than (ii) because air from the low speed bypass holes (at the throttle butterfly) provide
    air to mix with the fuel into the Pilot fuel air circuit.

    The reason why I am going into this detail is to emphasize the importance of (ii); when the choke
    isn't used, (ii) is the circuit solely responsible for starting the engine (and it was manufactured with a
    defect).
    The balance I referred to earlier is important (The low speed jet, the pilot fuel-air screw, and the spring
    rate are all balanced), and it is important to understand each type of pilot circuit, and how it works with
    the low speed circuit.


    Bill M.
    Last edited by wmazz; 08-04-2013 at 07:46 PM.
    Horsepower == Speed, RPM != Speed



  5. #25
    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
    What do you run for the data acquisition? Other than a mini tach, how can I verify I'm actually getting full Rpm?
    I don't have a good answer for that. I hate tiny tach's! My best tach was the size of a small calculator, and I
    bought it from Suzuki. It was available in their special tool line.

    I have thought about doing an open source data acquisition project, but my free time is about to run out.

    If I find something decent, that doesn't cost a fortune, I will let you know. But if that isn't a problem, just
    go here.


    Sincerely


    Bill M.
    Horsepower == Speed, RPM != Speed



  6. #26
    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!

    What is your issue with Tiny Tachs? My brother and I run the max RPM hold versions on a couple of our skis. While nice they don't always give an accurate picture. Sometimes for example they'll throw out a value of 10,000 rpm.. when the rev limiter is set no more than 8000. We try and always glance at the tach while riding, which can be kind of dicey on some of them. And that's one reason I haven't put a tach on my 550/750.

    Also getting back to pop off pressure and my question, how would you adjust for aftermarket flame arrestors on a stock engine with no leaks?

    And lastly, what was the mid 3rd jet meant to accomplish? No one seems to know, as most of the performance guys deal strictly with Mikunis.
    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 [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



  7. #27
    PWCToday Newbie
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    Re: Jetting Guru's! Dual 3 jet Keihin CDK2 40's help!

    This thread has great info. I am have trouble with my 750sx with dual Keihins, it has developed a bog when I blip the throttle past 1/4. It bogs terribly and falls on its face. How do I check/diagnose leaks in the carb? I have torn them apart and have 125/72/45 jetting in them now with AM FA, Coffman pipe, decked head, etc.

  8. #28
    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!

    I would put money that its a lean hesitation from too high of a pop off, and not a bog. I thought mine was a bog but a bigger jet cured it! I would put in a 50 mid jet, or the shortest springs and that should improve things.

    I was just out on my 550 today, and I have 72 50 135 with the low screw at 1 5/8. Last time out I had the low screw at the stock 1 turn setting, but today I had low hesitation right off idle and increasing the low screw has substantially fixed it.

    Ride around just prior to the pipe coming on. Then after a minute pull full throttle and see what happens. If it hesitates terribly put in a bigger mid jet or shorter spring. Do same test with ski going so slow you can barely stand up. Do it for a minute. Then pull full throttle. If it hesitates, increase low screw by 1/4. If its worse then its rich, go the other way.

    Post up your results. It will be nice to have a good collection of data here.
    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 [45.8mph gps]
    1987 WJ650:
    6M6, JD Intake Grate, 17/20, cheater pipe [47.8mph gps]
    1994 XiR: 830cc Superstock, PJS side draft, 13/18 swirl [53.7mph gps]
    1998 SXI PRO:
    3DR hull mods [TBD]



  9. #29
    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 theVetteman3 View Post
    What is your issue with Tiny Tachs? My brother and I run the max RPM hold versions on a couple of our skis. While nice they don't always give an accurate picture. Sometimes for example they'll throw out a value of 10,000 rpm.. when the rev limiter is set no more than 8000. We try and always glance at the tach while riding, which can be kind of dicey on some of them. And that's one reason I haven't put a tach on my 550/750.
    Sea doo part #529 014 500 is just like my Suzuki tachometer. SeaDoo also makes a tach the size of a
    tiny tach, except it has an adjustable length of inductive wire.


    Also getting back to pop off pressure and my question, how would you adjust for aftermarket flame arrestors on a stock engine with no leaks?
    I will get back too this

    on a stock engine with no leaks?
    It Doesn't Exist!

    And lastly, what was the mid 3rd jet meant to accomplish? No one seems to know, as most of the performance guys deal strictly with Mikunis
    I will get back too this, but it is going to be a long detailed response.

    I could use some help with some photos.

    When I am done, I might publish a pdf copy, and start a Blog.



    Bill Mazz
    Last edited by wmazz; 08-16-2013 at 09:53 PM.
    Horsepower == Speed, RPM != Speed



  10. #30
    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!

    Does anyone have some good pics of their 3 jet carbs?
    Horsepower == Speed, RPM != Speed



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