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  1. #31
    PWCToday.com Is My Home Away From Home
    Join Date
    May 2007

    Re: Death at 4K... pop off or jetting?

    Also Bill, to address your feelings towards primers and chokes. I have to disagree there also, the fuel selector is a problem waiting to happen in a few ways, its why we bypass them. With the primer a couple Squirts and it starts instantly no matter how long it's been setting saving battery, starter, bendix and starter button, ....

    If people did what Factory recommended like shutting off fuel selector, chokes would be fine to have on a ski, tell me how many does that?

  2. #32
    PWCToday.com Is My Home Away From Home
    Join Date
    May 2007

    Re: Death at 4K... pop off or jetting?

    Dub post, sorry. PWC is act I ng funny tonight.
    Last edited by driftmaster; 09-14-2017 at 03:25 AM.

  3. #33
    PWCToday.com Is My Home Away From Home wmazz's Avatar
    Join Date
    Jul 2013
    Riverside, CA
    Blog Entries

    Re: Death at 4K... pop off or jetting?

    On Yamaha's, they have funky Mikuni carbs with small low jets (when you consider the
    carb size, the seat diameter used and the spring). Despite this I have always found that
    Yamaha's run as expected when all their vacuum leaks are repaired.

    A fuel primer example:
    If you install a fuel primer on a JS550 with leaking main seals, and
    the other possible problems associated with 550's. You may help the starting, but the
    original problem still exists (Fr main seal is still leaking), and as a result the 550 engine is
    still going to die after you fall off, while the ski is in the process of circling back to you.

    On the Yamaha, all it's normal vacuum leaks are located on their complicated intake manifold
    and need to be fixed.

    Fuel selector valves and fuel tank pick-ups get blamed for all kinds of seeming lean piston
    seizures. People like Klemm have all kinds of nutty ideas on how to prevent these problems.

    Professionally I have only seen 1 specific fuel selector create problems, and that was on
    the XP800 and early 785 models that used the same fuel selector as the 89' SP.

    I realize that some types of fuel line cause problems, and I have replaced lots of fuel line
    over the years. But those fuel lines clogged the Mikuni internal fuel filters.

    Yamaha and Kawasaki use the highest quality fuel lines, and I don't recall any problems
    similar to SeaDoo.

    Quote Originally Posted by driftmaster View Post
    Yes, if we are recreational riding we do want to boat that will idle for a mile and take off without hesitation.

    On a closed course it's another story, you'll be in last place with that setup.

    As an example:

    Back when Bad Bones first started, they specialized in modified 44BN carbs with drilled
    out low speed bypass holes. There is 3 by-pass holes on the 44bn (one is actually a
    mid-range by-pass hole) and they drilled all 3 to .040" and added a fourth .040" hole
    between the top and middle holes.

    These carbs accelerated like a rocket! But they loaded up on the starting line, and unless
    you could keep the rear of the ski out of the water, they loaded up on the start line. The
    PJS race team manager used to copy this horrible mod and sell it to PJS customers. But if
    you leave the 2 bottom holes at .024" and drilled the upper 2 to .040" the carbs still had the
    same arm jerking performance, and could idle at the start line without loading up.

    I tune on two mod X2's. One is a Super Cylinder powered mod with Keihin 3 jet carbs. The
    other has a Dasa ported 750 mod cylinder that we modded for better overall and top end
    power. That engine runs a set of reverse jetted mikuni Sxi-pro carbs with 1.5 seats and
    115gr springs. The PJS boat is the fastest of the 2, but the modified Dasa with 55psi pop-
    off on SBN-I carbs has hole shots at the races and wins.

    Quote Originally Posted by driftmaster View Post
    I'm sorry, I just don't get or understand your drop test, I'v read it.
    I would really appreciate it if I could contact you via PM, so that I could rewrite that
    portion of the Blog

    I want to share the experience.

    I used that method to tune 440's/550's in our first decent test tanks in the early 80's
    to the end of my career tuning twin engines in Yamaha and SeaDoo jet boats in a very
    large test tank.

    I have used the same method to re-jet or tune skis in lakes and rivers, and Mission Bay.
    On all the race sit downs and stand-ups and stock or limited skis.

    Back in 1979 we power tuned 440's in a horse trough. I have been using the same
    method since ~82 or 83' to present, and the only thing that has changed is the rules
    for the new style carbs, 86' CDK2, ~91 SBN, ~94' SBN-I that all have the same type
    of pilot circuit. The Walbro carbs actually had a fixed low jet and a pilot circuit similar
    to the newer carbs. The BN's and old snowmobile carbs like Tillotson, Keihin had low
    speed circuits.

    If you are unfamiliar with pilot circuits look at any ~80' and up Kawasaki, Yamaha,
    Honda, or Suzuki motorcycle carbs. The all have pilot circuits fed by the low jet
    and adjusted by the pilot screw below or in front of the throttle butterfly. The pilot
    circuit port is located under or in front of the throttle butterfly, and only controls
    starting and idling.

    Low speed screws are located above, or behind the throttle butterfly.

    Bill M.


    I apologize for hijacking the thread.
    Last edited by wmazz; 09-14-2017 at 08:55 PM.
    Horsepower == Speed, RPM != Speed

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