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  1. #11
    Resident Guru zpilot's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    Thank you for the feedback Vetteman & Bill.

    According to Coffman's, the current TS/SC pipe made its peak HP@ 6000 rpm. I can trust this information to be accurate but some other info like Peak HP for the Viper 9000 can be questionable. I'm referencing a magazine article on the Thunderjet F-2 800 Vette provided a while back (See attached.) The bore info is incorrect so the Peak HP could be also.

    Regarding port timing, I spoke with John Newsom from Jetski Haven years ago and he said the following. (Only info I have)

    "I do know the port timing and all in that engine will not let it run much over 6500 rpm's. The engine has most of its power on the bottom and mid range. To transfer some of that power from the mid to the top you will have to raise the port timing. That is what we discovered when we started building these engines with the Kaw 750 base (Case & Crank) it raised the port timing up 2mm."

    Right now with my current setup with the Big Hub 10/18 swirl, 12 vein magnum pump, Rip Turn 87mm reduction nozzle I peak 47-48 mph @ 6490 rpm. It gets there very fast, quicker than my XIR.

    2012-10-25_21-34-45_279.jpg





    1995 Kawasaki SC

    PJS Viper 9000 800cc
    PJS Exhaust Manifold
    Coffmans Full Exhaust
    Custom Jetinetics Flywheel/drilled ring gear
    12 Vein SS Magnum Pump
    10/18 Skat Track Swirl Impeller
    PJS Rip Turn
    DG Intake Grate






    1994 Kawasaki XIR
    Group K Head Mod
    PJS Exhaust
    Skat 9/17 Big Hub Swirl
    UMI Bars

  2. #12
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    ----------------------------------------------------------------------------
    I made a mistake at the bottom of the page, so I corrected the mistake here.
    -----------------------------------------------------------------------------
    Sorry for the late reply. I have not spent as much time here like I used to.

    From what you have told me, one impeller size is not going to increase the rpm enough.
    I expect more changes will be necessary.

    I would bet the pilot screws (low speed screws) are too rich. They rob the engine of peak
    rpm.

    But I am not saying to start with the carbs, as that can be dangerous when you have an
    rpm deficit greater than 500 rpm.

    Because the SC has a greater wet hull area than an SX or SXR, the impeller size is different.
    Even the X2 needs a smaller impeller or a different set-up.

    Would you elaborate on how your engine is set-up. I don't recall if the 9000 came with Mikuni
    38 SBN's or Keihin CDK2's. Do you know the jet specs?? + it was a long time ago.

    Do you know the exhaust timing? ~192' exh duration would require 7100 to 7300 rpm, and
    186' exh duration would require 6800 to 7000 rpm.

    Is your Coffman the TS exhaust system?

    Quote Originally Posted by zpilot
    Would I gain more rpm & speed if I go down to a 9/17? I like the bottom and mid performance and don't want to loose too much of it but would like a few more mph
    on on top or to get close to peak performance/speed. I'm open to going with a smaller compression nozzle if needed.
    Good bottom and mid performance is typical of an over pitched impeller.


    Once you have a set-up that exceeds your rpm goals, then you start fine tuning the pump,
    and nozzle sizes. But in the beginning we start with the largest nozzle size possible.

    One method for fine tuning the pump, is increasing the pitch on the leading edge to increase
    acceleration.



    Bill M.

    On the 2 race X2's I work on, I believe they have modified 750 sx swirls repitched to 10/17
    (one of the X2's has the same 12 vein pump). Both have similar large exit nozzle diameters.
    A PJS X2 nozzle (but not the turning nozzle) and an open Solas nozzle.

    I have also been impressed with the performance with 20:1 Maxima 927 over normal oil ratio
    like 40:1 & 50:1. Generally I recommend (to avoid unwanted problems) using small impellers,
    big nozzles, 20:1, and at least a decent tachometer while finding a good set-up.

    Back in the 90's, pitch gauges were not common. So I used mm's as a guideline for pitch/rpm
    changes. Roughly speaking 1mm off the trailing edge and some improvements with the carb
    tuning and exit nozzle diameter should get you in the ball park. Less work if the exhaust
    duration is less than 192'. <---- Mistake!

    It should read " Less work if the exhaust duration is ~186'."


    Horsepower = speed.

    And the proper balance of HP and impeller = reliability.

    ================================================== =========

    Note: just read your last post: If the Coffman TS pipe makes peak HP at 6,000 rpm, subtract
    500 rpm from my rpm estimates.

    186' = 6300 rpm, 192' = 6600 rpm.
    ================================================== =========

    I would still like to hear about your carburation?
    Last edited by wmazz; 02-20-2018 at 01:37 PM.
    Horsepower == Speed, RPM != Speed



  3. #13
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    Obviously you are closer to your goal, than you thought. A good dose of tuning
    and you will have a good baseline.


    As I recall the jetting on the Mikuni 38 sbn's from Performance Jet Ski used cut
    115 gr springs.

    Knowing the screw settings would help, and jet settings if possible.

    The Performance Jet System reed blocks were not a very good design. Have you
    replaced the petals yet, and if so what brand or type are they?

    Did you replace the Performance Jet System main seals before you installed the
    engines?


    BM

    Increase the baseline rpm, then tweak the pump for more speed or acceleration.
    Last edited by wmazz; 02-20-2018 at 02:22 PM.
    Horsepower == Speed, RPM != Speed



  4. #14
    Resident Guru zpilot's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    Thank you Bill.



    -----------------------------------------------------------------------------
    Sorry for the late reply. I have not spent as much time here like I used to.

    From what you have told me, one impeller size is not going to increase the rpm enough.
    I expect more changes will be necessary.

    I would bet the pilot screws (low speed screws) are too rich. They rob the engine of peak
    rpm.


    The carbs are dual Keihin 38's. I plan on upgrading these eventually. Its been a while regarding jetting specs but I remember it came from the factory with 90 low & 120 high and I believe I had to go down to 78's for the low to get it running. I definitely would be better off with 80's since I am currently 2 1/2 turn on the low and 3/4's on the high. The transition between 1/4 to 1/2 throttle is a sudden leap in speed. No smooth transition.



    But I am not saying to start with the carbs, as that can be dangerous when you have an
    rpm deficit greater than 500 rpm.

    Because the SC has a greater wet hull area than an SX or SXR, the impeller size is different.
    Even the X2 needs a smaller impeller or a different set-up.

    Would you elaborate on how your engine is set-up. I don't recall if the 9000 came with Mikuni
    38 SBN's or Keihin CDK2's. Do you know the jet specs?? + it was a long time ago.

    Do you know the exhaust timing? ~192' exh duration would require 7100 to 7300 rpm, and
    186' exh duration would require 6800 to 7000 rpm.

    No Clue, but I'm assuming it could be 186 or less.

    Is your Coffman the TS exhaust system?

    Yes, TS/SC same pipe called Coffman's Sensation

    Quote Originally Posted by zpilot
    Would I gain more rpm & speed if I go down to a 9/17? I like the bottom and mid performance and don't want to loose too much of it but would like a few more mph
    on on top or to get close to peak performance/speed. I'm open to going with a smaller compression nozzle if needed.
    Good bottom and mid performance is typical of an over pitched impeller.


    Once you have a set-up that exceeds your rpm goals, then you start fine tuning the pump,
    and nozzle sizes. But in the beginning we start with the largest nozzle size possible.

    One method for fine tuning the pump, is increasing the pitch on the leading edge to increase
    acceleration.



    Bill M.

    On the 2 race X2's I work on, I believe they have modified 750 sx swirls repitched to 10/17
    (one of the X2's has the same 12 vein pump). Both have similar large exit nozzle diameters.
    A PJS X2 nozzle (but not the turning nozzle) and an open Solas nozzle.

    I have also been impressed with the performance with 20:1 Maxima 927 over normal oil ratio
    like 40:1 & 50:1. Generally I recommend (to avoid unwanted problems) using small impellers,
    big nozzles, 20:1, and at least a decent tachometer while finding a good set-up.

    Back in the 90's, pitch gauges were not common. So I used mm's as a guideline for pitch/rpm
    changes. Roughly speaking 1mm off the trailing edge and some improvements with the carb
    tuning and exit nozzle diameter should get you in the ball park. Less work if the exhaust
    duration is less than 192'. <---- Mistake!

    It should read " Less work if the exhaust duration is ~186'."


    Horsepower = speed.

    And the proper balance of HP and impeller = reliability.
    Last edited by zpilot; 02-20-2018 at 02:19 PM.





    1995 Kawasaki SC

    PJS Viper 9000 800cc
    PJS Exhaust Manifold
    Coffmans Full Exhaust
    Custom Jetinetics Flywheel/drilled ring gear
    12 Vein SS Magnum Pump
    10/18 Skat Track Swirl Impeller
    PJS Rip Turn
    DG Intake Grate






    1994 Kawasaki XIR
    Group K Head Mod
    PJS Exhaust
    Skat 9/17 Big Hub Swirl
    UMI Bars

  5. #15
    Resident Guru zpilot's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    Quote Originally Posted by wmazz View Post
    Obviously you are closer to your goal, than you thought. A good dose of tuning
    and you will have a good baseline.


    As I recall the jetting on the Mikuni 38 sbn's from Performance Jet Ski used cut
    115 gr springs.

    Knowing the screw settings would help, and jet settings if possible.

    The Performance Jet System reed blocks were not a very good design. Have you
    replaced the petals yet, and if so what brand or type are they?


    Did you replace the Performance Jet System main seals before you installed the
    engines?BM
    Seals and Reeds are the factory setup, I have not touched them.





    1995 Kawasaki SC

    PJS Viper 9000 800cc
    PJS Exhaust Manifold
    Coffmans Full Exhaust
    Custom Jetinetics Flywheel/drilled ring gear
    12 Vein SS Magnum Pump
    10/18 Skat Track Swirl Impeller
    PJS Rip Turn
    DG Intake Grate






    1994 Kawasaki XIR
    Group K Head Mod
    PJS Exhaust
    Skat 9/17 Big Hub Swirl
    UMI Bars

  6. #16
    PWCToday.com Is My Home Away From Home beerdart's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    20:1 thats a lot of oil any problems fouling plugs.

  7. #17
    Resident Guru zpilot's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    I've been using Klotz R50 since break in and usually run about 40:1 to 32:1 and have fouled plugs once but for the most part OK.

    Not sure on the 20:1 Bill recommended, sounds like a break in ratio to me.





    1995 Kawasaki SC

    PJS Viper 9000 800cc
    PJS Exhaust Manifold
    Coffmans Full Exhaust
    Custom Jetinetics Flywheel/drilled ring gear
    12 Vein SS Magnum Pump
    10/18 Skat Track Swirl Impeller
    PJS Rip Turn
    DG Intake Grate






    1994 Kawasaki XIR
    Group K Head Mod
    PJS Exhaust
    Skat 9/17 Big Hub Swirl
    UMI Bars

  8. #18
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    Quote Originally Posted by zpilot View Post

    The carbs are dual Keihin 38's. I plan on upgrading these eventually. Its been a while regarding jetting specs but I remember it came from the
    factory with 90 low & 120 high and I believe I had to go down to 78's for the low to get it running. I definitely would be better off with 80's since
    I am currently 2 1/2 turn on the low and 3/4's on the high. The transition between 1/4 to 1/2 throttle is a sudden leap in speed. No smooth transition.
    2 1/2 turns out on the lows is a rpm killer. You need to find a good setting near
    1/2 to 1 turns out. But first you need to determine what the carbs need. In order
    to figure that out, you need to learn the idle drop test.

    It would help to know about the main seals and reeds before you adjust the carbs.

    Keihin carbs are sensitive to changes on the lows, depending on the diameter of the
    low speed by-pass holes.

    Upgrading the carbs:

    My first thought is a pair of Kawasaki, or Polaris Keihins that are equipped with the mid-
    range circuit. The Polaris carbs can run richer jetting and have 2.0 seats. But they would
    be more difficult to adapt.

    The best carbs (IMO) are 38mm sbn-i carbs from a SeaDoo 720. The 720 has a similar
    short stroke and ~same size pistons. The 40mm sbn-i from a 785 will work too, but the
    785 also has a longer stroke.

    Either SBN-i carbs set-up with reverse jetting would be a boost in performance. On the
    800cc race X2's I mentioned, we run a set of Polaris Keihins on the super cylinder engine.
    The Keihins are nice because they are easily removed. On the DASA ported 800, we use
    SXR Mikuni reverse jetted SBN-i.


    Quote Originally Posted by zpilot View Post

    No Clue, but I'm assuming it could be 186 or less.
    If you are feeling industrious, remove the head and measure the deck height, and where
    exhaust port opens. Send me that info, and I will calculate the ex port duration.


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



  9. #19
    Resident Guru zpilot's Avatar
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    2 1/2 turns out on the lows is a rpm killer. You need to find a good setting near
    1/2 to 1 turns out. But first you need to determine what the carbs need. In order
    to figure that out, you need to learn the idle drop test.

    Sounds familiar, might have done this with setting up triple carbs on cars. I'll look it up.


    It would help to know about the main seals and reeds before you adjust the carbs.

    All original Seals and Reeds from PJS. I have not touched them



    If you are feeling industrious, remove the head and measure the deck height, and where
    exhaust port opens. Send me that info, and I will calculate the ex port duration.


    I would like to do this but getting head gaskets is a bit of a challenge. I see one one on Ebay for sale with the head off let me see if I can get them to send me the info.
    Last edited by zpilot; 02-20-2018 at 04:00 PM.





    1995 Kawasaki SC

    PJS Viper 9000 800cc
    PJS Exhaust Manifold
    Coffmans Full Exhaust
    Custom Jetinetics Flywheel/drilled ring gear
    12 Vein SS Magnum Pump
    10/18 Skat Track Swirl Impeller
    PJS Rip Turn
    DG Intake Grate






    1994 Kawasaki XIR
    Group K Head Mod
    PJS Exhaust
    Skat 9/17 Big Hub Swirl
    UMI Bars

  10. #20
    PWCToday.com Is My Home Away From Home wmazz's Avatar
    Join Date
    Jul 2013
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    Riverside, CA
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    Re: Impeller Direction Pitch Down or Up for More Top Speed Based on Peak HP

    Quote Originally Posted by zpilot View Post
    Sounds familiar, might have done this with setting up triple carbs on cars. I'll look it up.
    The process is similar to setting pilot screws on a car, but a water craft needs to be under
    a load. Specifically a low idle. I prefer ~1000 rpm. The idle should be low enough to hold
    your hand behind the pump. If a smooth low idle isn't possible the first time, adjust it twice.

    Are you familiar with the differnce between low speed and pilot screws. Carburated street
    bikes have pilot screws (most of them have no access unless you remove the plug that
    covers them).

    Fuel screws (like Mikuni BN low speed screws) require 1/4 turn out from the point where the
    engine stumbles and wants to die, or does die.

    Fuel-Air screws (like Mikuni SBN, SBN-i, or Keihin SDK2 pilot screws) require 1/2 turn out from
    the point where the engine stumbles and wants to die, or does die, under a load, at a low idle.

    Depending on what point (in turns out) where the engine stumbles and wants to die, or does
    die, it is easy to determine the proper low jet size for your application.

    Because jetting starts with the low speed jet, it is easier to estimate the main jet size.

    Quote Originally Posted by zpilot View Post
    All original Seals and Reeds from PJS. I have not touched them
    PJS main seals are red colored on the metal side. Kawasaki are green colored on the metal side
    of the seal.

    If you have the red main seals, they are the worst of the worst. I read about the supposed
    horror stories about ethanol affecting main seal and chuckle, but PJS seals are the real deal.
    Ethanol will melt, soften them until there is nearly no seal left.

    If you have these red colored seals, it is important that you take care of them because leaking
    main seals will affect the carburation. Especially the pilot screw settings that can rob you of
    peak rpm.

    Kawasaki reed cages have a rubber layer near the tip of the reeds, but PJS reeds have no
    rubber on the ends of the reed cages. We used to be concerned about premature wear
    to the PJS reeds.

    Mostly I was concerned that you may be loosing peak HP, if you replaced the PJS reeds with
    Boyesen dual stage reeds.

    Quote Originally Posted by zpilot View Post
    I would like to do this but getting head gaskets is a bit of a challenge. I see one one on Ebay for sale with the head off let me
    see if I can get them to send me the info.
    Isn't your head gasket copper? If it is, it can be reused many times so long as it is annealed.

    PJS heads were machined with less clearances between the head studs and stud holes, and
    that makes a PJS head more difficult to remove when compared to a Kawasaki head.


    Bill M.

    I might have a few gaskets still, I need to look.
    Last edited by wmazz; 02-20-2018 at 09:12 PM.
    Horsepower == Speed, RPM != Speed



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