1998 Sportster cavitation issues or...?

[coletrain777]

Hey all,
So I purchased a 1997 Sportster that is in great shape. I just took it out on the water for the first time the other day and I have what I believe to be cavitation issues. The engines run great, idles well, and both have good compression (all four cylinders between 147 and 150 psi). The problem is that when I take off under heavy throttle you can hear/feel the engine rpm speed up like a cluctch slipping in a car. I am pretty sure this is cavitation from what I have read. Also, the boat on smooth water at almost full throttle will on run around 41 mph or so. When I am at high rpm (6200 plus) and I give the engines more throttle their speed increases but the speed of the boat does not (also what I believe to be a symptom of cavitation).

So what say the experts...

1. Does this sound like cavitation, and if so where should I start looking?

2. What steps should I perform systematically to make sure that I am covering all the bases so that I don't have this problem the next time I go out. I am about 50 miles from water so I would like to make sure I am doing it right without just buying all new parts if I don't need them.

I am very mechanically inclined (do motorcycle and auto mechanics) just not very familiar with boats, let alone jet boats. An help/guidance is greatly appreciated. Oh, and I do have a factory service manual.

Thanks Cole

 

[coletrain777]

Also, the boat's reverse doesn't really work... I would say almost no movement.

 

[fastboatman29212]

I own a 1997 Speedster. Is your Sportster a 1998 or a 1997? Not that it matters much.

There are others who are more knowledgable than me, but you will need to measure the gap between the wear ring and the impeller with a feeler gauge. If the gap is larger than specification, the the impeller becomes inefficient at pushing water out through the rear nozzle, all resulting in a loss of power.

Read what Seadoosnipe says in his post: http://www.seadooforum.com/showthread.php?4958-quot-How-a-jet-pump-works-quot

Read what Dr Honda says in this post: http://www.seadooforum.com/showthre...g-and-impeller-clearance&highlight=cavitation

Here is a link showing how to change the wear ring. http://www.seadooforum.com/showthread.php?30720-How-To-Changing-Your-Wear-Ring&highlight=cavitation

If the impeller has any substantial dammage, replacement impellers are available and fairly inexpensive. Here's a link to a company that supplies impellers (exchanged for yours). http://www.shopsbt.com/

With reverse not working, I would first check that the reverse gate is dropping down properly. That can be checked while on the trailer. As far as I know, that is the only device on the boat that can actually make your boat go in reverse. Even if you had a serious cavitation problem, the jet of water through the nozzle should cause the boat to back up as long as the reverse gate is down in proper position.

(I recently had my reverse gate removed for a jet pump oil change and found that there is a lock mechanism that will hold the gate in the up position. I doubt that your problem is related to something like that (accidently in the locked position) because then the control lever would not allow you to shift it into reverse.)

Let us know what you find out.

 

[coletrain777]

Sorry for the post confusion it's a 1998 Sportster.

 

[mlebauer]

I have a 2001 Challenger with twin Rotax 717s, 170hp. I've got similar symptoms.

Your issues don't sound severe. You may want to replace the wear rings for peak performance, that's the most obvious source of sub-optimal performance. They're the black plastic sleeves around the impellers. You can see them from the back by shifting to forward and shining a flashlight into the outlets. From the front if you crawl underneath you can see them through the intake ports, which are covered by your weedless grates. Opening the weedless grates allows you to get a flashlight in there to shine on the surfaces. If they're scored and you see uneven gaps between them and the impeller blades you may need to replace the wear rings.

My engines both seem to be running well after changing spark plugs. But I had a severe cavitation issue last out on the water when pulling away after idling near shore, and different feeling vibrations from the starboard engine. Boat wouldn't plane. I stopped, reversed and revved the engines, then shut down and restarted. I saw some torn pieces of black sheet like material in the water next to the boat. Could that be wear ring material? Started again and got the cavitation and vibration, then some buzzing sound. Then the boat took off and planned, running well up to 40mph. I didn't try to push it faster. Later, after a stop, I experienced the same symptoms, cavitation, then after stopping it ran well, but this time I didn't see anything in the water. This time I pushed it to full throttle but couldn't get more than 40mph. Before it topping out at 50mph.

As to reverse, mine doesn't reverse well either, but the gate seems to be dropping down normally when out of the water.

When I looked at the impellers after getting home the wear rings appeared to have some scratches but I couldn't see any unevenness in the gap either from the front or back. The impellers have a few nicks and rust spots but nothing severe. The blue sleeve on the starboard engine is mostly gone, on the port engine it's mostly there but for the last 1-2 inches before the impeller. Shaft is fairly rusty on both sides.

Sorry to interject in your thread, but it's relevant to my situation. If someone has some suggestions to what I am experiencing please comment.

 

[coletrain777]

I am going to go out and take a look at the wear rings and attempt to measure the clearance (have to modify a feeler gauge to get it long enough to reach inside). How do I tell if the carbon ring is good or needs replacing???