Carbon seal issue causing cavitation on ‘97 GTX?

[Jasondpals]

I have a new-to-me ‘97 GTX 787 that will not accelerate from a stop. If you floor it, the RPMs jump to 8k and the jet ski doesn’t move very fast. if you gently work your way up to on-plane, it can go 40-45 mph. I suspect it’s cavitation from somewhere, but when I look at carbon seal symptoms online, I don’t have any of them besides cavitation. I dont get a lot of water in the hull nor do I have the black line on the inner hull. Am I fixating on the ring too much? I’m thinking I’ll replace it since the part is only $40. What else could it be? The impeller appears to have pretty good tolerance to the wear ring. There are no shark fins ahead of the impeller to remove.

 

[POPPS]

To rule out the carbon ring, back the ski into the water securred on the trailor,,start and rev ,,,see if water comes in,,,
I am suspecting the wear ring is gouged or the prop is messed,,post a pic please.

 

[Jasondpals]

 

[Lothsahn]

With symptoms that bad it doesn't sound like carbon ring. Carbon ring can do what you describe but usually less severe.

When you say "pretty good tolerance", what does that mean? You really need to measure with feeler gauges as these tolerances are extremely critical. It's a bit like saying "there's just a small hole in a suction cup and I don't know why it won't seal."

I suspect your problem is too much of a gap on the wear ring or a damaged impeller. It doesn't take much damage to make the impeller stop working.

Looking at your pictures, the impeller isn't in great shape.. I don't know if that's enough damage to cause those stmptoms. It's hard to tell if the wear ring has too much gap. I think it does.

 

[artr]

I had a similar problem on my 96 GTX. I did not had a water leak from the carbon seal but noticed that the original rubber boot that holds the seal and provides pressure to seal the carbon ring against the stainless steel hat was easy to move. I took the carbon seal out and found some dark spots on the surface of the stainless hat that felt smooth but turned out to be pitting when viewed under magnification. Replaced hat, carbon seal and boot and the issue was resolved. Even though no water leaked, air was getting into the jet pump under hard acceleration from the carbon seal/hat interface. You may also want to put a neoprene seal ring where the jet pump mounts to the hull (even though the parts list does not call for one) because that is another place where air could get into the pump to cause cavitation.

 

[POPPS]

Check the splines on the drive shaft,,,pto carrier.

 

[Jasondpals]

To follow up after a long ebay shipping SNAFU, I smoothed out the impeller with a die grinder AND replaced the carbon seal with a new kit from ebay. I was surprised and how much more flexible the new boot was than the old one and thought that it wouldn’t be stiff enough to work, but I took it out on the water yesterday and it jumped right out of the hole and ran well for an hour. It’s a bummer it took till the end of the season to get the ski in shape, but I’m excited for next summer

 

[AKnarrowback]

That leading edge damage on the impeller was enough to create the performance issue you are describing.

Just as an example. For an experiment I took the impeller out of my 94 xp with a clean factory leading edge. I spent a half hour and took the factory edge, ground, filed and polished all three to a knife edge on the leading edge and was very surprised at how much it improved the hole shot.

It only takes the slightest dent in the leading edge to set off the efficiency of the impeller. The leading edges must be sharp to have the machine run right.

As a note. You can replace the carbon seal with a regular double seal carrier assembly that was on the earlier generation DOOs. I went on ebay and found the carrier/seal assembly with the rubber hose from a 94 GTX and put it in my 97 GTX while still using the 97 drive shaft and no modification to any parts. It's personal preference as to which seal type you prefer. I like the double seal carrier, but if neglected on greasing it there can be damage to the hull fitting if the bearing locks up.