Kawasaki engine in a Seadoo GTS
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  1. #1
    I dream skis pacificmariner's Avatar
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    Kawasaki engine in a Seadoo GTS

    I bought a Kawasaki 750SS to play in the surf, but it's not as much fun as an X2. I tried it on an ocean cruise last year, 140 mile fun ride, but porpoise all the way. A friends Seadoo did the same ride comfortably, but working on a Rotax is never easy. For instance lets say I want to change the headgasket. Kawasaki, handful of nuts, head off, gasket change, torque down, good to go. Rotax you'll be awhile, plus the whole oil lines thing. The GTS has everything nicely centered making for a balanced ride, lots of storage space, and a bigger fuel tank by 4 gal. I've got buckets of Kawasaki parts and a free GTS hull so I figured why not.

    First thing was the bed plate. Rad Dudes has one for $250, but couldn't say if it would fit a '96GTS. Using a tape measure and a paper template I drilled the bed plate for the 750 engine. Minor shimming lined it up with the driveshaft.

    I measured the length the coupler would have to be to fit the driveshaft properly. The coupler was turned out to allow a press fit of 1" round stock that was threaded to fit the Kawasaki Crankshaft. A local gunshop built 2. I'm hoping the extra weight might help the Kawasaki idle smoother, but if I lose RPM I'll go to the lighter one.

    Next, throttle linkage. 1"x3" flat stock properly drilled was the easy part.

    I used the SS handlebars, throttle cable, e-box, and wiring. The Seadoo oil, and fuel sensors work with the Kawasaki wiring.

    The pump came off a '94 XP with a Skat Trak 15/20 impeller because I had one. The pump has trim that I will install later.

    The GTS had only a fuel gauge with an oil light, there is a blank hole next to it, and the hood was cracked. A '92GTI donated a nice single gauge hood, seat, handlebar clamps, and air intake tubes.

    An X2 donated the exhaust. I used rubber hose, and some PVC to run the exhaust out the Seadoo waterbox.

    It's been out for a short trial, and does well even with a badly worn wear ring.

    The wear ring has been replaced, minor leaks repaired, another test is planned. If it runs as expected then the exhaust will be turned 180 to avoid a mile of hose. Also the Seadoo e-box will be used since it snaps into place, with longer leads so it can be serviced outside of the engine compartment. A cover for the coupler, and the extra holes in the bed plate filled in.
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  2. #2
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Lake tested today at 42mph. The heavy coupler affects the top end, won't come up to full RPM so the small one will replace it. Forgot to add that the purpose of this build is to make an economical cruiser. High speed/hole shot isn't important, comfort/mileage is. Will keep the single carb as that got about 10mpg in the SS hull. The large Seadoo engine bay is nice, pulled the engine start to finish in a 1/2 hour with little fuss.

  3. #3
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Note the original, and the modification.

    The X2 exhaust was given a 180 so the outlet faces back into the Seadoo waterbox. The adapter is roughed out. If it tests good then a better one will be made.

    On the expansion chamber, the inlet was cut on the weld, rotated 180, and rewelded. It's important to cut on the weld that way there is enough metal to weld too. Use the cast exhaust pipe that has a hose connection to the expansion chamber to allow some movement. The mounting bracket on the exhaust manifold must be cutoff. I probably won't use a bracket unless vibration becomes a problem.

    I'm concerned that the adapter may get hot. If that happens then I'll drill passages in the next one, and feed water from the weep hole thru it.
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  4. #4
    Top Dog wire4money's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Your speed is not too far off. In 97 with the more powerful 720, it was a mid 40 mph boat. The 720 is 85 hp, so with a small pin 750, your speed seems about right. If you need more rpms, repitch the impeller.


    Sent from my iPhone using Tapatalk

  5. #5
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Thanks for the impeller tip.

    In the first pic notice the original weep hole outlet faces the head on the repositioned pipe. I drilled/threaded for 1/8" pipe a new fitting. To avoid short circuiting the cooling water I positioned it opposite the inlet. The original outlet will be plugged.
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  6. #6
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Something important I forgot to mention. The Kawasaki crank doesn't stick out as far as the Seadoo so I cut some round stock to slip inside the coupler, and that gives something for the rubber bumper of the drive shaft to ride against.

    Weighed the large coupler and it comes in at 4lbs, I don't feel it helped this engine run any smoother so the small one will go on.

    Fitted the pipe today, plenty of room, and lines up with the waterbox.
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  7. #7
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Lake test today. The exhaust adapter works and doesn't get overly hot, but I will drill it for cooling anyway. the RPM is back up with the smaller coupler. I put on 10.5 miles, used about a gallon of fuel, with a nice smooth ride. Mileage is about the same as the SS so the larger fuel tank will extend range by about 30+ miles Next is the e-box swap, and connect the fuel/oil gauge. Also for ease of fuel filling in "foreign" ports the auto oiler will go back on.

  8. #8
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    I noticed cavitation on the last ride that got worse toward the end. Turned out the driveshaft is slightly bent, and that ruined the carbon ring letting air into the pump. New shaft and replaced the seal with the older greaseable type, and reset the engine for better alignment, probably end up having to get the proper tool. Anyone know what the driveshaft end play is? Not something covered in the manual for obvious reasons.

    Seadoo gauges seem to need 12 volt input to work. Hoped to plug it into the e-box and have them come on with the engine, but may install a switch instead. Picked up a new coil with longer leads to allow e-box service outside the engine compartment. It may be easier to cut the Seadoo e-box and put the Kawasaki e-box in it rather than fabricating mounts for the Kawasaki components.

    As an added note the exhaust pipe to manifold bolts are fine thread, but in this town I could only find course thread tapered head screws so the manifold was re-threaded with no apparent problem. Also use a proper countersink drill otherwise the tapered screw head won't have enough metal to grip and will work loose.

    Back to the lake for another try.

  9. #9
    PWCToday.com Is My Home Away From Home iangdesign's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Cool build...
    You are not acting like the person Mr. Rogers knew you could be...

  10. #10
    I dream skis pacificmariner's Avatar
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    Re: Kawasaki engine in a Seadoo GTS

    Thank you.

    Lake test, side by side with another GTS, mine a is a little bit slower but overall handling is the same. Engine/exhaust noise about the same though I've got a rattling pump I will deal with later.

    The exhaust adapter gets to hot too keep a finger on and the 1/2" thickness is not enough to drill cooling passages so the next one will be 3/4" . Also I created the adapter on a drill press and should have drilled the center hole first that would have made it easier to get an accurate center on the bolt holes. It's slightly off center and tends to blow the gasket and spray water out, might be happening inside too.

    I mounted a Kawasaki tilt/trim switch assy. and will use it to run the fuel/oil gauge and the bilge pump on demand. I don't trust the Kaw. electronics to keep up with a constant demand for 12 v and who stares at their fuel gauge anyway. Later when the tilt/trim unit goes on it will get changed.

    So far this build has cost about $400 only because I had so many parts and scrounged from junk machines when I find them. Look forward to taking this on a long ride and see how it compares to others.

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