98 Jet Ski only 25 mph

[bethcor1]

Please help. I am out of ideas.

I have a 98 Jet Ski 750 STx that will only run 25 mph and I believe it should go 45-50.

I put in a SBT block, rebuilt the carbs and replaced the fuel pump. ( I have run the carb and fuel pump set up on another ski w/the same SBT block and it runs 50+)
I cleaned out the fuel tank and replaced the pick up tube assembly and the on/res switch.
The impeller clearances seem to be ok.
The machine seems to not rev as high as it should from 2/3 to full throttle there is no change. The butterflies open to full through the range and the choke butterflies are wide open.
I thought it was the overheat sensor holding the revs down and swapped it with one from another ski, no change.

I have 150 psi compression and good spark in both cylinders.

Any ideas out there???

Thanks

 

[JUSTINTIME]

Re: 98 Jet Ski only 25 mph

sounds like the high speed is not set right

 

[bethcor1]

Re: 98 Jet Ski only 25 mph

I have switched the carbs/fuel pump set up to another ski with the same SBT motor and that machine ran 50+, so I do not think it is in the carbs.

Thanks for your reply.

 

[Jeff Walkowiak]

Re: 98 Jet Ski only 25 mph

try switching the coil and plug wires from the other ski,, kawasaki is notorious for corroded plug wire cores and it will cut out one cylinder as it warms up,,

 

[bethcor1]

Re: 98 Jet Ski only 25 mph

I switched the complete box of electronics from another ski that runs 50+, still only 25 mph. No change in performance from 2/3 to full throttle.

Help.
What else is left?

 

[JUSTINTIME]

Re: 98 Jet Ski only 25 mph

impeller seems to be ok???

 

[bethcor1]

Re: 98 Jet Ski only 25 mph

Yes, the impeller is new and the clearance appears OK. The revs do not change in the last third of the throttle range even though the butterflies open to WOT.

 

[Jeff Walkowiak]

Re: 98 Jet Ski only 25 mph

having eliminated the ignition and the compression, leads back to the carbs or you did not get the timer base correct when you did the engine,, I would be checking the timing and re looking at the carbs or reed valves, does fuel blow up out of the carbs when you run it fast?? try running with the seat removed, and the air box off, when it starts to lag, give it a quick shot of starting fluid in to the carbs, if it picks up quickly,, you know the thing is starving for fuel, if it boggs out you have some other problem.