1990 sn 650sj ride plate/intake grate

[Denver21drake]

I have a 1990 superjet and mainly ride rivers and rapids. My ski cavitates a lot and Im thinking it because I have the stock intake and ride plate. The rest of the ski is stock as well besides a custom aftermarket handlepole I’m currently building. Any suggestions on ride plate and intake grate if that is my issue, or other suggestions to fix my problem?

 

[pineapple]

a new prop will help alot

 

[Denver21drake]

a new prop will help alot

Any suggestions on one? I don’t really know much about the aftermarket impellers, but I know there’s like 9/10 ect. And I’m assuming different ones impact torque and top end differently

 

[pineapple]

Anything is better then a stock prop I've heard that the newer superjet one work good but 9-15 hooker will be the best bet with your boat

 

[mikidymac]

As others have said, the stock aluminum impeller is junk and if your's is original it is probably even worse. That is where your poor hookup and cavitation is coming from.
Pretty much anything is better, the Hooker 9/15 would be the best if you have the money, second would be a stock 2008 superjet impeller. From there an old Skat 9/13 or 14/18 or even a stock Waveblaster 1/WR 3 GP impeller.

 

[mthomps]

Does your ski cavitate when ripping around on flatwater and mild river conditions or just in rapids

 

[Denver21drake]

Does your ski cavitate when ripping around on flatwater and mild river conditions or just in rapids

Just in the rapids. It porpoises pretty bad on flat water when I try and give it full throttle but from my understanding I just need to learn to position my self better to avoid that

 

[TheBuzzard]

airiated water causes cavitation with all stock pumps. that why the mag pump was used. you can ride right up the guy in front of yous ass and you wont lose power. if the rapids are full of air bubbles, its going to cavitate. props spin on air and bite on solid water. a top loader intake grate might help stuff the pump better. if you ride with somebody with a top loader, put it on and see if it helps.

 

[mthomps]

Just in the rapids. It porpoises pretty bad on flat water when I try and give it full throttle but from my understanding I just need to learn to position my self better to avoid that

Its also throttle control. You want the pump drinking water at all times. Learn to feel when the pumps gonna leave the water and let off the gas for a half second to dig the pump in again.

 

[Th3 VVay]

I've struggled with porpoising on my ski since I've owned it. I don't go full speed often so it hasn't been a big deal, but it is still annoying at times when I do. I've own the ski for 5 years so its not just from being a newbie. I can get all of my weight past the bars and it will still do it. I added a scoop grate which did not help. I added a +90mm ride plate which improved it slightly but it still occurs. At this point I'm convinced that its because the rear foam is waterlogged. I put off de-foaming it this year to freshen up some other things. But at the end of this season I will be cutting the tray and redoing the foam. Since you have a 90, thats likely your problem (or a contributing factor) as well. All superjets, especially the early years are known for getting water under the tray and the foam absorbs it and weighs the back end down.

 

[mthomps]

Please dont cut up your ski and gut the tray thinking new foam will solve it!! It would be easier to lose 25lbs off your body!

 

[Th3 VVay]

Please dont cut up your ski and gut the tray thinking new foam will solve it!! It would be easier to lose 25lbs off your body!

I only weigh 155lbs as is, so losing 25lbs isn't my problem. And I've ridden my friends stock RN superjet and I can ride it just fine, no porpoising at all. So its something with my ski. And he has the same porpoising problem when riding mine. Why would you recommend not cutting up the tray and de-foaming? Theres plenty of threads of people doing just that. Aside for being a possible cause of the porpoising issue, my ski probably weighs at least 25lbs more than it should from waterlogged foam. Getting rid of that and replacing with a closed cell foam only has benefits as far as I'm aware.

 

[mikidymac]

I would agree, if you have the time and suspect a water logged tray why wouldn't you fix it? It will cost you about $100 in materials plus turf. I am not saying it will fix all problems but that weight and water should not be there.

 

[Th3 VVay]

I would agree, if you have the time and suspect a water logged tray why wouldn't you fix it? It will cost you about $100 in materials plus turf. I am not saying it will fix all problems but that weight and water should not be there.

I just came to the conclusion this is likely my problem last year. Over winter I needed to do some other maintenance (midshaft rebuild, carb rebuild, replace some gaskets, fix some electrical gremlins, among other things). So they tray tear down was last on my list since it is rideable as is. As mentioned, I plan to tear into it this fall once the season is over now that the other items have been sorted.

 

[Jhucke]

I just came to the conclusion this is likely my problem last year. Over winter I needed to do some other maintenance (midshaft rebuild, carb rebuild, replace some gaskets, fix some electrical gremlins, among other things). So they tray tear down was last on my list since it is rideable as is. As mentioned, I plan to tear into it this fall once the season is over now that the other items have been sorted.

Good luck, but I really doubt this is your problem.

 

[Th3 VVay]

Good luck, but I really doubt this is your problem.

Then what do you suspect is the issue?

-Its not weight (155lbs)
-Its not rider error (been riding 5 years and I don't porpoise on my buddy's stock SJ at all)
-Its not intake grate (have run with my scoop grate on and run with no grate at all, still porpoises)
-Its not the ride plate. Tried a stock one and now my new extended plate.

So to me that really only leaves waterlogged foam. Is there something else you suggest I check?

 

[Jhucke]

I've struggled with porpoising on my ski since I've owned it. I don't go full speed often .

-Its not rider error

-Its not weight

Hmmmmmm.... These posts are conflicting with your theories, reasoning, and sense of skill.

I'm going to say you don't know how to ride your ski own ski, sorry! Everyones superjet is waterlogged.

 

[mikidymac]

Hmmmmmm.... These posts are conflicting with your theories, reasoning, and sense of skill.

I'm going to say you don't know how to ride your ski own ski, sorry! Everyones superjet is waterlogged.

So he knows how to ride his friends ski that doesn't do it but he doesn't know how to ride his own ski? This makes no sense at all.
If you know what it is then just come out and tell us since he has tried everything else and is looking for help.

 

[Jhucke]

So he knows how to ride his friends ski that doesn't do it but he doesn't know how to ride his own ski? This makes no sense at all.

Have you ever been on a ski that you couldn't instantly ride really well? Also his buddies RN could be a 08+ that hooks up like crazy with pump position set back, nose glued down all the time compared to an old superjet.

I have no idea how his ski is built, it could be a POS mess in the pump area, not to mention could be a crappy stock prop or something. It is not waterlogged foam causing this, like I said, everyones superjet is waterlogged.

 

[Th3 VVay]

Hmmmmmm.... These posts are conflicting with your theories, reasoning, and sense of skill.

I'm going to say you don't know how to ride your ski own ski, sorry! Everyones superjet is waterlogged.

Whatever man, I thought you actually had something constructive to say towards the post. You say my theories are conflicting but don't explain how?

I don't ride full speed because its a superjet, I like freestyle riding, jumping boat wakes (chasing them is when the porpoising is annoying), and working on tricks.

You claim rider error, but that doesn't make sense as to why I can ride a friends stock Superjet and not have the problem. Its a 2002 by the way, not an 08+ with the new hull design and pump. I can lean over my bars with my feet at the front of the tray and it will still want to do it. I can regain control by backing off throttle a bit but when trying to go flat out, after a bit it starts again.

Pump is in good shape. New pump shoe seal, clean vanes, newish 9/15 hooker. Did it with my old skat trak prop as well.

Anyhow, I still don't understand the pushback to defoam. Worst case scenario it doesn't fix it and my skis 25 lbs lighter. It will make it faster and easier to jump out of the water, not seeing the downsides here. Google superjet foam porpoising and you'll see other posts of people having a similar issue that went away after replacing foam.