SBT Jetski Engines, Parts & Accessories

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  1. #1
    Joined
    Jun 2003
    From
    Phoenix, AZ
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    27

    Post

    My wife's bone stock Kawasaki 1987 650 SX seized last year after the original oil injection line broke. Only one piston seized, and it was a light seize (I almost just sanded the piston and freed the rings). I rebuilt the top end, but it won't run right? It starts and seems to have power for the first 300 yards then looses power to the point that at full throttle it will only reach 1/3 throttle RPM's. The ski was working great before it seized.

    I have checked the following:

    -The compression is 135 each cylinder.
    -It has new plugs (B7ES).
    -Took carb apart and all is well.
    -Verified plug wires are making good contact.
    -Verified there are no exhaust leaks.
    -Getting good water flow.
    -Verified fuel pump is working.
    -Crank felt normal when replacing pistons.
    -Crank case drain is sealed

    I have not checked the following:
    -Reeds
    -crank seals
    -Timing/stator

    So my question is, could the reeds and/or crank seals have been damaged when it seized? Would bad reeds or crank seal cause it to run the way I described?

    What do you suggest I check?

    Thanks!

  2. #2
    Joined
    Jun 2004
    From
    Spring Hill, Fl.
    Posts
    149

    Post

    your fuel fump may be good, but check to make sure that the fuel filter isn't running out of fuel because of clogged fuel pick-ups in the tank. It may be o.k at idle, but when higher rpms demand more fuel, the flow may be restricted just enough to cause your problem.... rob
    ride it like you stole it

  3. #3
    Joined
    Jun 2003
    From
    Phoenix, AZ
    Posts
    27

    Post

    Thanks Rob,
    I'll check the filter, but to ski ran great before it seized, so I would be suprised if it clogged that fast (not over time).

  4. #4
    Joined
    Jun 2004
    From
    Spring Hill, Fl.
    Posts
    149

    Wink

    10-4 that. Sorry, I thought you said it had been laid up for about a year. My bad. Still couldn't hurt. Suggested it because it sounds like a lack or fuel or possibly not enough spark advance, (the latter I don't know how to diagnoseon a ski). What was the cause of the cyl siezure? Rob
    ride it like you stole it

  5. #5
    Joined
    Jun 2004
    From
    Spring Hill, Fl.
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    149

    Post

    Sorry, reread your thread- oil line failure. Don't mind me....
    ride it like you stole it

  6. #6
    Joined
    Jun 2004
    From
    Spring Hill, Fl.
    Posts
    149

    Wink

    Hey one other thought for you...You said it rode great before the seizure, and now, rebuilt, it doesn't. A two stroke motor crankcase must be sealed while alternately under pressure and vacuum,(primary compression). Check for a bad jug (cylinder)base gasket, (especially since it was off recently),or a crack in the casting of the bottom section of the block and jug. Both could cause lack of primary compression. A compression test does not show you the lack of primary compression. You must seal all engine openings, carb intake, exhaust, vaccuum ports, etc, and then pressurize the case, then look for a leak-down of pressure. It still does not explain the running well for 300 yards and then a bog down.... rob
    ride it like you stole it

  7. #7
    Joined
    Jun 2004
    From
    Spring Hill, Fl.
    Posts
    149

    Post

    P.S. If you have access to compressed air blow through the fuel supply line back towards the tank, I am thinking that the pick up screen is clogged, not the fuel filter. Try to switch to reserve and see if the same problem exists. If the pickups are clogged, from crap in the tank, the reserve sits lower, and may be even more clogged, making the problem more evident....rob
    ride it like you stole it

  8. #8
    Joined
    Jun 2003
    From
    Phoenix, AZ
    Posts
    27

    Post

    Thanks Rob!

    The base gasket is new and the cases looked good, but it's a thought. I'll try spraying some WD-40 around the base of the cylinder, if there's a leak the RPM should go up. I was also thinking low end leak, that's why I was asking if a seize could damage the crank seals. Bad crank seals would also cause a leak, yes?

    I do have compressed air, so I'll try blowing trough the pick up line this weekend.
    Thanks,
    Doug

  9. #9
    Joined
    Jun 2004
    From
    Spring Hill, Fl.
    Posts
    149

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    "Bad crank seals would also cause a leak, yes?"

    Yes it could/would, however, I don't think that the siezure specifically would cause the seals to go bad, but the overheating due to the oil loss would certainly be the prime suspect for any rubber parts (seals) to fail. Since you've described the siezure as a light one, I really don't feel like I'd tear the lower end apart for the problem you've got, It would be my last option. I really think that the motor would run piss-porly at idle if there were primary compression leak from the lower end, and it would never get you onto plane. Also, because of the compression/vacuum with every revolution, I am not so sure the WD40 gimmick will work, but it is worth a shot.
    I've was an auto technition for a long time, (recently changed feilds) so I gotta tell ya, I've seen more fuel injected cars that have had a lack of power, that stall, that buck, that miss, that other shops had mis-diagnosed (at $50-$80/hr) as a "mysterious computer problem" smoke a very costly electric fuel pump due to a clogged efi filter, than I can count. I always look for simply stuff first. My gut instinct still says it's a lack/starvation of fuel. I don't know if a full fuel filter and carb bowls may get you full throttle for 300 yards, but ???? who knows? I'm sorry to sound like a scratched, scratched, scratched, record.... (lol).... but I will be the first one to publicly admit that I was wrong if that is not the cause.....It just seems like the most logical place to start,(at least to me). rob
    ride it like you stole it

  10. #10
    Joined
    Jun 2003
    From
    Phoenix, AZ
    Posts
    27

    Post

    Thanks Rob!

    I'll let you know what I find!
    Doug

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