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  1. #1

    Join Date
    Jul 2009
    NW Arkansas

    First jet-ski build.

    A bit of background information on myself and the ski: We bought the thing brand new back in 97, a 96 slt780. Ran great for years, fast 'enough' and a comfortable 3 seater to boot... not to mention it handles better than any other 3 seater ski I've ridden. About 4 years ago the stator went out... replaced that. Then the MAG cylinder decided to explode... big end rod bearing exlploded, ground into cylinder sleeve piston, and gashed the head. Also ruined the crank pin and split the case! It was only a few weeks ago that I finally got around to getting a new case for it.

    Me, I'm a hardcore 2 stroke enthusiast- and love building motors for power. The last thing I built was a 2000 ktm 380exc (dirtbikes are my true passion) I did so much trick custom work myself its not even funny... but this isn't a forum about dirtbikes. So to make it short... I'm pretty handy with a dremel; and I deeply understand the innerworkings of 2-strokes and what changes make them better and how. I'm new to the jetski modding world, but I'm not worried about that too much... its just a large 2 stroke with near-infinite cooling right?

    So... now its time to rebuild my jetski motor. They were rated at 93 h.p. stock... not bad- its gonna be much better though. I am rebuilding the motor with pretty much all OEM parts, of course the majority of which will be hand modified by myself.

    Here's what I'm going to do/ have done.

    1.)New case... actually bought a whole new "ready to run" motor off ebay... what a joke, The thing was seized and had a pound and a half of rust in it. IT had to of been sunk in salt water and left to rot.
    But the new case is actually an older case... With a lower internal case volume. It doesn't have the pointless "pre-ports"(not entirely sure what they are really called) leading from the reed cage to the side main intake ports. Completely pointless- only thing they do is increase crankcase volume (bad on a two-stroke). So the "new" case is a mod in and of itself.

    2.) Ported intake manifold... that thing sucked in its stock form, really.

    3.) Remove choke flaps in carb and install a primer kit.

    4.) custom air filter/spark arrestor...

    5.) ported/blueprinted reed cage stuffers.

    6.) blueprinted cylinder to case mating

    7.) Port and polish I don't want to get too detailed in the description here.

    8.) Custom built silencer (aren't they called waterboxes on these things?) replacement.

    9.) some hull modifications for increased airflow- I've heard these skis sometimes starve for air... so I'm sure it will after these mods.

    10.) 785 PRO CDI (looking for one... i have several 780 cdi's on hand too...)

    11.) Oh yea, I forgot about the coated pistons... PC-9 Skirt coatings, and TBC ceramic piston tops. From Swaintech.

    12.) I'm also thinking about adding some swirling singh grooves.

    Over the winter I'll probably polish and re-pitch my prop... and get a either a Solas or R&D intake grate. And I'll be spraying it with some custom paint.

    This is pretty much just a leisure sea-couch (gonna leave it with reverse and everything)... but I can't just leave a motor stock during a rebuild. Keeping that in mind, any suggestions?

  2. #2
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Sounds like a plan keep us posted with pic's..

  3. #3
    Join Date
    Jul 2007
    Cedar Rapids,Iowa
    Trippple PSI Pipes,44 carbs

  4. #4

    Join Date
    Jul 2009
    NW Arkansas
    Quote Originally Posted by Keddano View Post
    Trippple PSI Pipes,44 carbs
    I was thinking about dropping in some 785 pro pipes and carbs... but I don't want to put in a smaller tank.

    Any other tripple pipes I'm afraid would cost too much. I may still go with new carbs though... or possibly just bore mine.

    After I build my next bike I'll probably build another ski- That will be the one I do the best of the best. (Probably 1200+ cc, DI, exhaust valves, tripple pipes, turbo)... but that is probably 3 years away or more, like I said, i gotta build my next bike first.

  5. #5
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    ... its just a large 2 stroke with near-infinite cooling right?
    With a multiple throw crank, cross contamination on your strokes, very strange carbs compared to other sports, and of course the biggie...

    your dirt bikes were barrrrrapping on and off the throttle quite a bit. Most watercraft are pegged near the limiter in their over-rev state, 95% of their life while bouncing up/down the limiter like a crazed crack-junkie.

    Think about that last one, as you wield your dremal.

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