Seadoo sportster cavitation

[Bradley007]

Hello first post on the site!!! First I'd like to say hello and Thank you in advance for all the time you guys delicate to helping others with their issues...

I currently have a 1997 seadoo sportster and had it out on castaic lake in Ca. I was driving around for about 2 hours the boat was running fine, switched seats with a friend and the he accelerated but when he got to around 12-15 mph the boat started vibrating and would rev up but not go any faster, I took the boat to a local shop that said I needed a engine mount so I had them put it in and took it back to the lake with the same issue so I took the boat to a different shop they pulled the pump and said there is a little dent in this thing that the impeller goes in front of (I don't know what to call this thing) it looks like a prop but it's not my question is would this slight dent cause cavitation if so I need to buy a whole new pump cause I don't think it comes out, I can post pics of the dent tomorrow. Thank you so much!

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[Coastiejoe]

Cavitation is caused by a few things. An impeller that is bent, (normally a dent is not an issue), a waer ring that is worn out, (to much space between the impeller and the wear ring allows for slippage), a shaft seal, (air gets sucked from inside the hull and passes through the impeller causing impeller loss of traction).

The shaft seal is a common failure. There is a few easy checks to narrow this down. I'm walking out of my house right now, hopefully someone will jump in to offer addition help for you...

 

[Dr Honda]

With your symptoms... you just ducked up a stick, or other trash. You may need a mount, but that's easy to check. Just grab the engine and try to rock it.

A small dent or clearance issue wont show up like that.

Lastly... you may need a new carbon seal. When they wear or get weak, the pump can suck them open, and that will draw air. In turn... you don't move.

 

[Bradley007]

Should I just change the shift seal, reinstall the pump and see how it goes or can you tell me how to test this seal?

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[Bradley007]

Btw impeller is fine wear ring is fine

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[Coastiejoe]

If impeller and wear ring are good, then yes, change the shaft seal.

 

[Bradley007]

I took the boat to a seadoo shop (all he does is repair seadoos)
He told me the shaft seal would let water in if it was bad... you think he's right?

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[Sportster-2001-951C-Stock]

If you are saying you can accelerate up to full speed slowly but if you nail it out of the hole the impeller ventilates and slips, then I'd say you're probably sucking air through the carbon seal. There's a rubber bellows that acts like a spring and pushes the carbon seal against the rotating stainless steel ring to make an air tight dynamic seal but as the rubber bellows ages, tension is lost. You might be able to adjust the bellows slightly to increase tension and see if the "cavitation" improves, then if it does, replace both pieces.

The other thing that sticks into my head would only be likely if you couldn't get up to speed at all, which would be the drive shaft splines in the PTO coupling may be worn out and stripped, in that case the motor would turn but the drive shaft wouldn't receive torque. So if you have the drive shaft out, inspect those splines carefully.

My jet pump isn't perfect. I've sucked up ski ropes, probably a couple handfuls of gravel, sand and sea shells through this jet pump and it will only ventilate the impeller if I nail it full balls to the wall in a hole shot pulling a slalom skier(I suspect this is normal ventilation under worst case conditions), this can be a challenge for many small boats. Instead, I have to finesse the throttle to pull up a slalom skier and it's more of a struggle than I'd like but it works, just can't nail the throttle.

Inside the pump, I can clearly see one of my stator fins behind the impeller is bent over slightly, the trailing edge on one of the impeller blades is slightly bent over as well, the leading edges of the blades are all dinged up and I can see swirl marks in my wear ring but the clearance is still pretty tight. Given all this, the jet pump still works amazingly well, I can hit 50mph with two people in the boat.

EDIT - And yes, the doc has a good point about having sucked up a stick or some trash into the jet pump, look it over carefully from in front and especially behind using a bright flashlight, if there's something in there it will not pump water correctly and vibrate like you describe.

 

[Bradley007]

Thanks I already checked the splines and are fine... I'm just going to get a new seal any recommendations? It's either a 96 or 97 Idk if the year matters or not

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[Sportster-2001-951C-Stock]

Thanks I already checked the splines and are fine... I'm just going to get a new seal any recommendations? It's either a 96 or 97 Idk if the year matters or not

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Well I guess you already checked for debris inside the pump if you removed the pump. I think all the carbon seals were the same, not aware of any changes. Get the rubber bellows too, they lose tension. I think you can have impeller ventilation before water leaking.

 

[Coastiejoe]

The seal can pass air before water leaks into the hull. That said, it is also common for the seal to allow water into the hull. If water does come in at the seal location then the seal or adjoining hardware is bad.