1993 GTX Cavitation, loss of propulsion, but good engine power

[a76vwbus1]

I have a 93 GTX. I'm new to jetski mechanics, but am very familiar with mechanics and motorcycles. I just bought this ride and got it running. Compression is 125-126 both cylinders. no oil leaks, fresh gas. Motor runs/idles great. Throttles up great (don't have tach so no RPM reading). Test in water....idle speed up to 1/4 throttle is fine, seems to have good propulsion, anything over that and it sounds like a slipping clutch(on a motorcycle). lots of engine power, not much forward movement. Looking at the water behind the machine I see that it is clear until i pass the 1/4 mark, then get highly airated (bubbly). Any suggestions on what this could be? I have checked the jet blades nothing that looks bad to me and the clearance between the rubber ring look tight, I need to get some feeler guages on it to see what it actually is. Air must be getting into the jet from somewhere?
Thanks,
Doug

 

[El Toro 33809]

It would either be the carbon seal on the drive shaft or the impellar/wear ring. The Clarence should be about the thickness of a dime or less

 

[LouDoo]

Your ski doesn't have a carbon seal, but it could be the carrier seal/bearing. It's more likely the wear ring, check the clearance .040". Also your compression is low, but this won't cause cavitation.

Lou

 

[Seadoobuddy]

Welcome Doug,
It could also be the seal between the pump and the hull. If it's sucking air, you will lose "speed".
Plus the items that El Toro mentioned.

The clearance of the impeller blade and the wear ring should be .04 inches.

 

[a76vwbus1]

Checked it today. .025 was tight between the ring and blades. I also checked the boot and bearing on PTO shaft, everything looked ok, but when i greased it grease came readily out of the engine side of the bearing. this leads me to believe that it might need serviced. The wear ring i'm not sure of. I'm going to water test again today and see if any change. oh, my compression gauge is old an off by 3-5psi, so i think it is more like 130psi, but I have read that anything over 110 is o.k. as long as there is not 10% difference between cyclinders

 

[a76vwbus1]

ok, like i said, greased bearing and retightened boot around hull, and bam....worked. tons of power, no cavitation. thanks guys. I'll post the next time and issue comes up!