engine revs high with no thrust

[andyfest0719]

I have a '98 Sportster 1800 with twin 720's. When I throttle up from idle to plane, one engine revs high (to limiter) but provides no thrust. The dealer thought there might be air leaking thru the drive shoe so I have had the drive shoe re-sealed on that side, but still have the same symptom . There are weeds in our marina that sometimes get sucked in - could that be the issue? Any other ideas? Many thanks in advance.

 

[scooper77515]

NO thrust, or just not enough thrust?

There should be SOMETHING going on back there, unless your drive shaft is not connected to the engine, or the impeller is gone.

 

[swill777]

Check the carbon-ring carrier assembly. Mine was sucking in air through there and cavitated BADLY, and you have the same boat I do. When you say no thrust, you mean you still see water flowing out of the nozzle to some extent right? If not at all, then yeah, your driveshaft isn't spinning. You can easily check that by just looking down in the water when it's running. Or, just pull the plugs, turn the pto wheel by hand, while someone looks in the pump with a flashlight to make sure the impeller is spinning... you can even have them jam a long screwdriver in there, while you try to turn the pto wheel, to make sure its not stripped out.
I would be you are just having cavitation, and its most likely the pump to shoe seal, that carbon-ring carrier seal, or the thru-hull seal. Sucks I know, been there!

 

[scooper77515]

I agree that you may be pointing him in the right direction.

When someone says "no thrust" I am hoping that they are just exaggerating...

Just wanted to make sure he didn't mean "none", rather than just not enough.

 

[andyfest0719]

thanks guys

Thanks all. I 'll check out all of your suggestions. I did exaggerate about "no thrust". There is some thrust, but a lot of cavitation that accompanies especially when if I jump on on the throttle from low speed. I can get up to a plane cleanly if I throttle up using moderation. When I find out what the problem is I'll let you know. I love the boat and want to fix it up and keep it, rather than trading for a new jetboat. We've had this boat for 7 years and it's been great. Sadly, the interior layout cannot be found anymore - BRP has gone to the dual cockpit layout only. It has about 200 hours on the engines now. Anything to keep my eyes open for besides compression?

 

[scooper77515]

In the 7 years, have you ever replaced the wear rings?

Check for wearring-to-impeller clearance (.040 max for mine, not sure for yours). I swap mine out every other year due to wear. It will behave like cavitation, lots of spin, but very little go.

 

[nswillin]

Just a good rule of thumb: High RPMS/No speed: Propulsion problem, wear ring impeller, etc.

Low RPMs/No speed: Fuel or engine problem, carbs, gunk, low compression

 

[seadoodude1]

Most likely you need a new wear ring. Check the clearance between impeller and ring.

 

[andyfest0719]

My first thought was wear ring too, so I had them both replaced last summer - unfortunately it did not solve the problem.

 

[swill777]

hey man, read my post again... I know its hard to believe, but that carbon-ring carrier seal (where your driveshaft couples to the PTO), where the boot is, can cause SERIOUS cavitation. I too put a new wear ring in, and still had horrible cavitation until I fixed the seal. It's worth looking at... just my .02

 

[andyfest0719]

Thanks swill - I'll check that out first.

 

[andyfest0719]

Thanks to all - update on cavitation issue with '98 Sportster 1800

Hi everyone and thanks for your help. Just to update you, my '98 Sportster 1800 was cavitating badly on one motor. I had the wear rings replaced on both sides and the drive shoe re-sealed on the side that was acting up, but with no improvement. I took swill's advice and replaced the carbon ring assembly last weekend when I got the boat out of storage. That fixed the issue. The old carbon ring did show a little wear. The replacement carbon ring, an updated version in the Bombie parts catalogue, seems to have more "meat" to it. Once again - thanks and have a great & safe boating summer.http://www.seadooforum.com/images/smilies/new/hurray.gif

 

[swill777]

Glad to hear you got it fixed an running... trust me, I KNOW how irritating that is. Have a great summer on the water.

 

[bombtech]

I have the exact same boat. Just got two new engines from SBT, rebuilt the pumps, new impellers and wear rings......still have cavitation. I'm thinking it's probably the same thing yours was doing, or it's worth a shot. I've replaced everything else. Where did you purchase your carbon ring?

Hi everyone and thanks for your help. Just to update you, my '98 Sportster 1800 was cavitating badly on one motor. I had the wear rings replaced on both sides and the drive shoe re-sealed on the side that was acting up, but with no improvement. I took swill's advice and replaced the carbon ring assembly last weekend when I got the boat out of storage. That fixed the issue. The old carbon ring did show a little wear. The replacement carbon ring, an updated version in the Bombie parts catalogue, seems to have more "meat" to it. Once again - thanks and have a great & safe boating summer.http://www.seadooforum.com/images/smilies/new/hurray.gif

 

[andyfest0719]

carbon ring purchase

I got the part from a Bombie dealer just down the road. The owner/mechanic is a good friend who lets me do some work on my own in his shop. You can also get the part in the on-line parts store here at Sea-doo forums. I looked up the carbon ring for my boat in the original parts catalogue. It turns out that Bombardier has updated the part and the part #. My dealer had several in stock as they are used on several different boats & PWCs. The new part is substantially thicker than the original. It can be a bit of a pain to replace - the hardest part was getting the "c"-clip off the driveshaft assembly. It did do the trick, however. Cost for the part was around CDN$55. Good luck!

 

[swill777]

I believe SBT has the part(s) as well as Parker Yamaha. You can also try to loosen the clamp... then take a look at how the carbon ring (part #14 in the diagram from the parts link at the top of the page) is contacting the seal carrier ring (part #8). They should be making good contact and there should be a decent amount of pressure on the seal carrier ring. You can push the hose protector (part #10), toward the pump, put more pressure on the assembly, then tighten the clamp. That got me by for a while. And it will point you in the right direction. If the thru-hull fitting (part #21) is bad, you'll have to replace that as well. It should not be sucking any air in around or thru that fitting. I believe SBT and Parker carry a "better" replacement one as well. Good luck.. Take pics and keep us updated.. I wish I had so that maybe it could have helped some more people out.

 

[garyguise]

Wear ring

I have an 06 Sportster 215hp. I think I may have a wear ring issue as well. I too have had a stick stuck in there, twice, and had to idle back to the dock. Now, getting up to speed takes feeding it throttle much to slowly for skiing etc. I didn't know there was a wear ring tho I'm glad it sounds like there is. How hard is it to replace? Is it a dealer thing even if one is mechanically inclined with standard auto and motorcycle tools? Is it shown anywhere in the manual?

Gary

 

[ncarbon]

I just did mine in my Speedster 200. First time, it was very easy. I think it was more intimidating than anything. I joined and downloaded the manuals here, read, studied and was surprised how easy.


Ned

 

[johnysbl]

So I hate to sound totally stupid, but what exactly is cavitation and how do you know when it is happening???

 

[speedsterdad]

Carbon ring replacement

What tool is used for small clamp at PTO boot? see attachment

 

[seadoodude1]

So I hate to sound totally stupid, but what exactly is cavitation and how do you know when it is happening???

Cavitation is when the jet pump sucks air and reduces thrust or water circulates in pump instead of being thrust out the nozzle. This can be caused by too large of a clearance between impeller and wear ring, damaged impeller and or wear ring, or sucking air into intake stream around pump to hull seal, between ride plate and hull, or around drive shaft and thru hull bearings and seals.

Symptoms are high reving engine without thrust, like the transmission is slipping.

 

[seadoodude1]

What tool is used for small clamp at PTO boot? see attachment

OEM is an okeiter clamp. Most just cut it off and replace with a small tie wrap. it is there only to hold the grease in the pto splines. plastic tie wrap works just fine.

 

[speedsterdad]

thanks. In process of replacing carbon rings and was unsure if needed on reassembly.

 

[seadoodude1]

You may not even have to take clamp off, drive shaft may just pull out of PTO leaving grease boot on PTO. no reason to take boot off.

 

[speedsterdad]

Thru hull seal and carbon ring

Has anyone heard of replacing thru hull seal and carbon ring assembly with a modified old school version that eliminates carbon ring and boot and has fixed sealed bearing and adding a neoprene seal between pump and ride plate? I am told by local repair shop this is the cause of all cavitation and will permanently repair cavitation issue.