Js550/750 or 650sx/750 conversion?
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  1. #1
    PWCToday Regular
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    Js550/750 or 650sx/750 conversion?

    I have a 95 750ss. It runs great (does start hard).
    Looks like someone jumped on it while it was sitting on rollers.

    I was thinking of swapping the components to a standup.

    Is one conversion easier or cheaper than the other?

    I found a couple bare hulls so I would need to use everything from my ski.

  2. #2
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    Re: Js550/750 or 650sx/750 conversion?

    I think that the 650sx to 750 conversion will be cheaper. You will just transfer motor and electrics. Maybe you will need another impeller afterwards depending on what you have in your ski, but at least you will have a running ski from the beginning. You can also use 650 electrics on a 750 small pin. For big pin engines I am not sure, some one who has tried it can advise you.
    For the js hull conversion you will need as extra a conversion plate for the motor and a high pitch impeller if you keep the stock pump. If you decide also a pump conversion then the cost rises even more.


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  3. #3
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: Js550/750 or 650sx/750 conversion?

    Since the case has the exact same mounting points as the 650 engine, the 750 drops right in the 650sx. I think because of that, and it's simpler to get an impeller, the 650sx/750 conversion would be cheaper. The 550 conversion either requires an expensive impeller with the oem pump (19 pitch with single carb, 20 with duals), or the Rhaas pump swap kit. The pump swap kit is a much bigger investment but it allows you to use much more common and cheap 750 impellers.

    These skis are two totally different animals. The 550/750 is more nimble, faster, accelerates harder, will have more low end.. pretty much more in every category than the 650sx/750. The 650sx/750 when built up well is a really great ski. Much smoother, but can still be made to have decent low end. It's a way better ski for carving stock hull to stock hull with a 750. It's more of a general purpose really great ski for the money. I had less invested in it than a mint stock 95 SJ in our group and most guys preferred it for the money.

    If you want something that's a bit wild and crazy and like your skis that way, do the swap on the 550. Get a set of oem 3 jet Keihin carbs that came on the ss xi skis, a 20 pitch impeller, ProWatercraft tubbies, and go nuts. If you want something that's a bit more mellow and easier for newer riders to learn on too, the 650sx/750 is a great option. Either way I would definitely recommend the dual Keihins and ProWatercraft tubbies. Good jetting settings are out there and you can get them for cheap. When set up right there about as good as dual Mikunis, at like 30% the cost. The tubbies really turn the performance around on these older hulls too.

    I have done both builds, if you're interested check the individual builds section by my username.
    Last edited by theVetteman3; 10-26-2018 at 08:13 AM.
    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. #4
    PWCToday Regular
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    Re: Js550/750 or 650sx/750 conversion?

    I had hoped to use my 750 pump on a js550 hull. I had recently found a bare hull for sale.

    After looking at the cost of the pump conversion, I may be better off finding a hull with a pump.

    It's been about 10 years since I owned a js550. If I remember correctly, they had a stainless wear ring in the pump. Is anyone replacing them or would I have to find a pump in useable condition?

  5. #5
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: Js550/750 or 650sx/750 conversion?

    Yep that's right. I would just find a good pump. I like buying matched pumps, as opposed to just a replacement wear ring/ pump front end piece. As the impellers wear in the ring they'll true it to the axis of the pump. Since you run high pitch impellers and need to get the impeller to wear ring gap absolutely as tight as you can for no cavitation, you need every benefit you can get in having an impeller that spins true. With my JS and SX pumps I would sand the wear ring in the high spots to make sure the impeller could fit as close as possible without rubbing.
    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]



  6. #6
    PWCToday Regular
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    Re: Js550/750 or 650sx/750 conversion?

    When doing a js550 conversion, what year hull js preferred?

    I had wanted a layer year because of the rear exhaust exit.

  7. #7
    PWCToday.com Is My Home Away From Home theVetteman3's Avatar
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    Re: Js550/750 or 650sx/750 conversion?

    That's down to personal preference, but I prefer either the 82-85 with the above waterline front exhaust, or rear exhaust. Makes for easier installation of the tubbies. Although if you request it, Prowatercraft will cut an exhaust slot for you.

    I really liked the front above bondline exhaust on my 85. It made the riding experience even more visceral- added sound, heat and everything. Just hearing that big engine burble at idle thru the Supertrap waterbox was such a great sound. And as an added tuning element, I could tell when my flow control valve was opening. Sometimes it's useful to see how much water is being dumped into the exhaust and when.
    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]



  8. #8
    I dream skis sportsfreak29's Avatar
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    Re: Js550/750 or 650sx/750 conversion?

    I have a js550/650 pump swap ski with a 650 motor, soon to have a PJS 9000 motor, with tubbies and footholds. It's a monster!

    I would recommend going the js route if you can afford it.
    If you're not crashing, then you're not trying!!!

    Ski situation in limbo!

    Special thanks to Chris Newmiller, and Mitchell at M&M Marine!

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