Much Cavitation and 10 mph top speed loss

[Seadoosam]

Just put in the 97 GTX 787 that i’ve been working on. I did have the pump off to check the fluid and everything and the wear ring and impeller didn’t loook that bad, but it is exhibiting the following symptoms:

WOT (I didn’t push it down and hold itfor a while because it was just put in for the season) comes at 42 mph and 6400 rpm.
V
ery slow to get into the 6k range even if I pin the throttle lever it just mosies on up there to 6k eventually

Tons of cavitation from idle when giving any decent amount of throttle up until it gets on plane.

Again, top speed 42 mph

This seems pretty low to me. Just looking for input. I think I need probably a new impeller and wear ring maybe based off other threads? Possible the WOT issue is a carb problem?

 

[JeremyD615]

Post a picture of your impeller. You normally just need a wear ring, but sometimes the prop will get dinged up and need some refurb. As for the top end performance, it definitely sounds like a carb problem. Sounds like it’s time for a rebuild and new fuel selector...

 

[Seadoosam]

Post a picture of your impeller. You normally just need a wear ring, but sometimes the prop will get dinged up and need some refurb. As for the top end performance, it definitely sounds like a carb problem. Sounds like it’s time for a rebuild and new fuel selector...

Is it me or does the impeller look like it’s up too high? not sitting in the wear ring enough. what could cause that? Thinking maybe yea carb problem. it starts so nicely without any choke tho. obv that’s different than running it well

 

[JeremyD615]

It definitely looks like it’s not all the way in there. Is there any play in it? Can you move it back and forth?

 

[Trooper182]

Your impeller looks like it is out too far. This is my 97 gtx impeller.

 

[Seadoosam]

It definitely looks like it’s not all the way in there. Is there any play in it? Can you move it back and forth?

Yea definitely seems high. Seems to have the normal amount of play. Maybe less than 1/8 of an inch of play. did PO put the pump together wrong perhaps?
Im pulling the carbs off as well. Thinking I might swap the pump for the one on my functioning 97 GTX just to see. Although that’s many trips to the ramp haha

 

[JeremyD615]

Go ahead and pull that impeller out and inspect the shaft and bearings. Somethings not right in that thing...

 

[Seadoosam]

Go ahead and pull that impeller out and inspect the shaft and bearings. Somethings not right in that thing...

at a loss. thought maybe he forgot the thrust washer, but it’s all here, shaft doesn’t look too bad either. bearings are great. it had no water in it. all oil. very confused. wear ring looks pretty good if u ask me too

 

[JeremyD615]

What’s the part number on that impeller? Maybe it’s been swapped at some point...

 

[Seadoosam]

What’s the part number on that impeller? Maybe it’s been swapped at some point...

i checked the impeller it’s the correct one for the ski. The only thing i noticed were the threads on the shaft were screwed up towards the end. i’m thinking maybe the PO didn’t put it on enough as a result. i used a shaft i had laying around from an extra pump (same type) and below is the result. It seems to have solved the high impeller problem. could the high impeller explain the horrible cavitation because it was barely making a “seal”?

 

[JeremyD615]

I would say that was your problem. Try it with the other pump and see what it does.

 

[Seadoosam]

That’s good to hear that was probably it Because I don’t know what else it would be has. Since I have the carbs off gonna rebuild those. I’m gonna put the pump back on with that new shaft and look at the carbs and I’ll update the thread when I water test again next week! Thank you

 

[Seadoosam]

Water test update! Between “fixing” the impeller and putting the missing membrane in the fuel pump in the carb, Getting 6610 WOT rpms. 48 mph gps. so much better than before! Think i’m dealing with the need for a wear ring and impeller at the moment still cavitates like a mofo can’t give it more than 4000 rpms of throttle or it cavitates. Feels like it hooks up at around 30-35 mph . Definitely running beautiful now though. Hopefully new pump parts will get me that little extra rpms at wot to get me closer to the 6800 normal

 

[Seadoosam]

New wear ring helped with cavitation. Now it’s back to not sounding right. only does 44 mph again. (gps). Believe it was spark issue. changed plugs wires and coil. still not sounding right and even hitting close to WOT. 6000 rpm max currently.