1990 JET-N-CATS Yamaha JetBoat by Hot Cats
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  1. #1
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    1990 JET-N-CATS Yamaha JetBoat by Hot Cats

    Picked up a what I assume is a very rare Project 1990 Jet N cats Jetboat thats powered By Yamaha mechanicals.

    Its currently Got the 500cc motor and the smaller 133mm JetPump in it unfortunately.

    I will be putting a 650 motor out of a Yamaha LX650 waverunner in it for sure.

    For those that know anything about these machines, My main question is:

    Will I be better off using the stock LX650 waverunner impeller in this boat or would a Skat Trak 15Y impeller offer better performance over the stock LX650 impeller??? These are the 2 impellers I have on hand and able to use.

    I also plan to grind down a unknown scoop grate I have laying around and retro fit it into the pump.


    Thank you for any insight provided.

  2. #2
    PWCToday.com Is My Home Away From Home fox river pwc's Avatar
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    Re: 1990 JET-N-CATS Yamaha JetBoat by Hot Cats

    The stock aluminum 650LX impeller is crap when new, but I'm not familiar with the skat 15Y. For the 133mm, I thought skat made a 15/18, 16/19 and 17/20??? And maybe a 14/17? I thought most Jammer swap builders were using the 16/19 or 17/20. I know the 650 Jammer I built for the 2019 Jet Blast 2019 raffle, I used the 16/19, and it worked very well. Had a high comp head when I built it, and now it has a pro-tec pipe as well, and that same prop is working nicely.

    If that jet N cat behaves anything like the 92-93 boston whaler Rages do, then you should expect to use/need a "one step steeper" impeller than the same motor would require in a WR500/650LX hull, as you may just burn a lower pitch prop due to the additional resistance that larger hull creates.


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    Re: 1990 JET-N-CATS Yamaha JetBoat by Hot Cats

    15 Y most likely stands for 15 straight pitch Yamaha.nYou are swimming in uncharted waters here ionstall the Skat 15Y and see what it does.
    Last edited by WFO Speedracer; 11-22-2022 at 12:01 PM.
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  4. #4
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 1990 JET-N-CATS Yamaha JetBoat by Hot Cats

    Your impeller choice should allow the engine to achieve peak HP.
    For example a stock 701 Blaster makes peak HP @6300rpm. Your
    15deg stainless steel impeller could be a good starting point because
    it is easy to repitch.

    If testing reveals the engine only revs to 5500 rpm, you could remove
    about 1mm (.040") on the trailing edge and gain ~400 to 500rpm. If you
    need a little more rpm removing about 1mm (.040") on the leading
    edge can gain ~250rpm.

    All you need is a vice and a large crescent wrench.


    Bill M.

    You could use a plastic pitch gauge instead, but who cares if you
    are using degrees or mm's, either one will do the job.

    Make sure the grate is sealed properly to prevent cavitation.
    Last edited by wmazz; 11-22-2022 at 05:57 PM.
    Horsepower == Speed, RPM != Speed



  5. #5
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    Re: 1990 JET-N-CATS Yamaha JetBoat by Hot Cats

    Does anyone know the Ideal Pitch that would work best(or close to best) on a boat like this? I can turn the 15Y prop I have into a variable pitch by bending the blades?

  6. #6
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    Re: 1990 JET-N-CATS Yamaha JetBoat by Hot Cats

    Quote Originally Posted by JettDreams View Post
    I can turn the 15Y prop I have into a variable pitch by bending the blades?
    No, not a variable pitch, you would just be making adjustments to
    your impeller to allow more rpm.

    But who knows, maybe the 15 will allow 6000rpm or so. The point
    is you should evaluate your impeller choice with a tachometer, not
    assume it is working properly.

    But, a bone stock engine without a tuned pipe is a forgiving set-up.


    Bill M.

    When DB (Pro-Tec) started modifying wr/wj 500's he used a 14 deg
    impeller. On your small pump, a 15 or larger should work for a 650
    without a pipe (Just in case).
    Horsepower == Speed, RPM != Speed



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