High RPM, low thrust on Low speed but good after 20 mph. Speedster 98.

[Mulder_den]

Speedster 98.
From 0 mph on full throttle both engines easy turn 7000RPM with very low thrust... Like some air in the jet pump and engines didn't get any load from jet pumps...
But after 20 mph RPM slows down to 5000 (still on full throttle), boat gets high thrust. Looks like jet pumps got water! RPM goes down because engine got load from jet pump.
Impellers looks good. New wear rings!

Any ideas? :-/

 

[Coastiejoe]

If the gap at the wear ring is good and the impeller is good, then you are getting air from the Carbon Seal would be my guess.

 

[Mulder_den]

If the gap at the wear ring is good and the impeller is good, then you are getting air from the Carbon Seal would be my guess.

Hmm... There are no any leak. But I'll doblecheck carbol seal today...

 

[Coastiejoe]

Hmm... There are no any leak. But I'll doblecheck carbol seal today...

It does not have to leak water in order for it to suck in air. It pulls the air from the hull as the water rushed by the seal and creates a low pressure area. It works off the Venturi Effect...

Some skis (and probably boats as well) leak air from the ride plate. Depends on how the pump is mounted..

 

[bobpilot]

I had the same problem with my 98 speedster, Renewed the carbon seal kits and bellows and now it is pulling like a steam train :thumbsup:

 

[utah997]

I had the same problem with my 98 speedster, Renewed the carbon seal kits and bellows and now it is pulling like a steam train :thumbsup:

Bob, how do you do this? I think this is the one last issue I have to deal with on my 98 Speedster. Rebuilt jet pumps, new wear rings etc. But seems like it's just a little light on the bottom end. Did you need to buy replacement parts or?

 

[BoLongo]

I live a couple of miles away from Impros; I had Dave repitch my impellers. So I took my carbon seals to him for his opinion. They looked like new to me. He showed me that the problem is actually on the inside where the shaft goes through the carbon seal, My seals were oblong on the inside from making contact with the shaft. If you think your boat has a lot of hours, it is probably best to replace just the carbon seal. I kept the steel part that makes contact with the carbon seal, and I kept my bellows.

 

[racerxxx]

I live a couple of miles away from Impros; I had Dave repitch my impellers. So I took my carbon seals to him for his opinion. They looked like new to me. He showed me that the problem is actually on the inside where the shaft goes through the carbon seal, My seals were oblong on the inside from making contact with the shaft. If you think your boat has a lot of hours, it is probably best to replace just the carbon seal. I kept the steel part that makes contact with the carbon seal, and I kept my bellows.

Challengers are notorious for mis alignment and egg out the insides. Engines need alignment. Saw the exact same thin on a repower I did a few years ago. I upgraded the guy to the OSD heavy duty carbon seals. they're the bomb. I even have on in my HX

http://osdparts.com/index.php?main_page=product_free_shipping_info&cPath=595_602_2&products_id=4


Stock hat vs OSD hat

 

[BoLongo]

One more thing to do :banghead: will it ever be done :ack:

Now I have to research how to align the engines. Hopefully, I can do it with the pump and shaft attached

 

[racerxxx]

One more thing to do :banghead: will it ever be done :ack:

Now I have to research how to align the engines. Hopefully, I can do it with the pump and shaft attached

Nope, you should buy the alignment tool. Other's have "made" their own homebrew tool, I for one own the correct alignment tool. Search your local craiglist for seadoo alignment tool.