650sx best mods for low end
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  1. #1
    PWCToday Newbie DudeWithAJet's Avatar
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    650sx best mods for low end

    I have an 89 650sx that I just got running good and want to get some nice low end power and acceleration. I already have a intake grate and a high compression head, and I donít know what should be on my list of priorityís.

    Thanks, Lucas

  2. #2
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 650sx best mods for low end

    Mod the stock pipe, instructions on several forums. Add a couple inches to the tail section of the pipe. Get a good aftermarket impeller. I have an old school Mako 16 pitch in mine. Mine also pulls pretty good with the stock 28mm carb. This alone will turn it into a different machine.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  3. #3
    Resident Guru
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    Re: 650sx best mods for low end

    Quote Originally Posted by DudeWithAJet View Post
    I have an 89 650sx that I just got running good and want to get some nice low end power and acceleration. I already have a intake grate and a high compression head, and I don’t know what should be on my list of priority’s.

    Thanks, Lucas
    The first thing you should do is take it apart and inspect/overhaul the entire boat. They always need seals and handle pole bushings. Plus you need to verify the crankshaft is not rusted and the pump and carrier bearings are quiet. Once the boat is in good shape the next question is, how big are you? If you are much over 150 then a larger engine is better than modifying a 650. It takes a pipe, porting, and an impeller pitched to near 7000RPM before they pull good and top 45mph. A 750 engine with the stock 650 pipe will have better response and go as fast as a ported 650 with an aftermarket pipe. The 650sx struggles with larger riders a lot more than a Superjet.
    Last edited by kweasel; 09-28-2021 at 03:29 PM.
    What exactly does the IJSBA do?

  4. #4
    PWCToday.com Is My Home Away From Home Benflynn's Avatar
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    Re: 650sx best mods for low end

    More compression, good impeller, sbn44, fiber reeds, cheater mod w/4-5” length added, h2o inj

  5. #5
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 650sx best mods for low end

    Quote Originally Posted by kweasel View Post
    If you are much over 150 then a larger engine is better than modifying a 650. It takes a pipe, porting, and an impeller pitched to near 7000RPM before they pull good and top 45mph.
    Not true. I'm 6'8" and 250#. My lightly modded 650sx with stock tiny 28mm carb will GPS about 43mph and gets there pretty quick with me on it. Stock non ported cylinders and red colored non modified head. Will outpull a stock 650 Superjet throughout the RPM range.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  6. #6
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 650sx best mods for low end

    Add a TS650 exhaust manifold to your set-up.



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



  7. #7
    Top Dog JC-SuperJet's Avatar
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    Re: 650sx best mods for low end

    Quote Originally Posted by wmazz View Post
    Add a TS650 exhaust manifold to your set-up.



    Bill M.
    Why is it better than the Stock SX Manifold? Is there a difference in Outlet Diameters?

  8. #8
    PWCToday.com Is My Home Away From Home Myself's Avatar
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    Re: 650sx best mods for low end

    Quote Originally Posted by JC-SuperJet View Post
    Why is it better than the Stock SX Manifold? Is there a difference in Outlet Diameters?
    Yes, it's a bit larger. And, it has a divider to keep the exhaust turbulance inside the manifold at bay.
    http://www.facebook.com/twinlakesjetskirepair

    '89 Kawi 650SX 42.4 GPS
    +3" stock pipe, ported ex. manifold, drilled waterbox, blueprinted pump, Ocean Pro ride plate

    '99 Yama GP1200 65U 61.8 GPS
    ported cylinders, matched cases, milled head, blueprinted pump, long ride plate

    '96 Seadoo HX 717 53.13 GPS
    light porting, massaged cases, lightened flywheel, port matched manifolds, Rossier pipe, stubby pump cone

  9. #9
    PWCToday.com Is My Home Away From Home Bionic racing's Avatar
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    Re: 650sx best mods for low end

    9/17 impellor , 81mm 750/800 reduction nozzel , modified shortened pump thrust cone , or the real short one that can be purchased , but top end will suffer with the real short one

  10. #10
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: 650sx best mods for low end

    The TS exhaust manifold has a diverter similar to an aftermarket
    exhaust manifold.


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



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