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Need help getting a Kawa STS 750 with new SBT engine to run correctly.

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  • Need help getting a Kawa STS 750 with new SBT engine to run correctly.

    Hi, I have a 1995 Kawasaki STS 750 with a new SBT engine. It way past break in, and while it runs smoothly, it is way short on power and will barely make 5600 rpm at wot.
    New sbt carb kits, rebuilt fuel pump, clean tank ect. This ski struggles to get out of the water with two medium size riders, and something in clearly wrong.

    While I am no expert, I rebuilt a Polaris slt 700 (3 seater, about the same size ski and engine) at the same time, and it screams, has good piston wash, responds to tuning, nice brown spark plugs, and so forth, with virtually no tuning.

    Clues:
    To get something that looks like piston wash, and avoid a low speed hesitation, I am turning the low speed screws out 1 1/4 and the high speeds out about 3 turns-way over factory specs. If I use the factory settings It sure does not seem like I am getting enough gas though it, the piston crowns seem dry and carbon coated. The single fuel pump has been rebuilt, ski starts like a dream with just a bit of choke.

    Pop off: well I tried to adjust this, used some lighter springs, and the ski would not do anything but idle. I put the stock springs back in and it runs and starts great, just low on power and rpms...

    Plugs: I noticed some light gray coloring on the insulators, but for the most part they stay pretty clean and wont do much of anything worth looking at. I have changed them, done plug chops, and pulled and adjusted the carbs so many times I cant even count them, the ski just does not seem to respond much to what i do.

    Pump: I have noticed some vibrations when I turn one direction under power that the Polaris does not do. I have not done much but look at the impeller, looks clean and not beat up, but I do wonder if some condition can exist with a pump that soaks up a lot of power and rpm from a ski? I have assumed that a worn out pump usually means a ski that revs high but just does not go forward like it should My Kawasaki hooks up and goes, just seems weak.

    Fuel Pump: Is there some test for these pumps, like measuring output on the return lines?

    Anyway, I am thinking a pressure test of the engine is my next move, any other ideas?
    thanks for any help.

  • #2
    Re: Need help getting a Kawa STS 750 with new SBT engine to run correctly.

    Your problem could be electrical, but spend some more time on the fuel system 1st. run a direct fuel line from the nipple on the fuel tank right to the carb, see if anything changes, also check your exhaust hose from the waterbox (muffler) the large diameter one that goes out to the exhaust outlet out the back of the ski. If this hose is restricting exhaust flow it will kill the skis performance some times the hoses delaminate from the inside out and block exhaust flow.
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    • #3
      Re: Need help getting a Kawa STS 750 with new SBT engine to run correctly.

      OK, I have looked at that exhaust hose before but I will really scrutinize it this time. Not jumping ahead, but as far as I can tell from the rebuild there was/is no timing adjustment on this ski, is that correct? It all seemed fixed in place with nothing to adjust, otherwise I would have been checking for retarded timing.

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