# Jet jon cavitation issues



## willholl79

I just recently purchased a 1436 jet jon with a 500cc Yamaha Waverunner engine. With just me sitting in the back driving, it will jump on plane fairly quick but still has cavitation issues. With another person in the boat it won't get on plane. The boat was built by the previous owner using the cut out hull section of the wave runner grafted to the jon boat. It's not the neatest rig in the world, but I plan on reworking some areas, if I can get cavitation under control.

This is my first experience with a "jet boat". I have had jet skis in the past. I am trying to figure out where to start with this issue. Is it the pump itself, weight, or angle/draft of the jet, not enough water in the intake, all of the above?

Any help is appreciated. This is a great site!


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## PSG-1

It could be several factors. Flat bottom boats don't exactly make ideal jetboats. Most jet skis and boats put the pump a couple of inches lower than the hull by forming a "spoon". Angle of pump and type of impeller could have an effect, as well.

I run a Yamaha MR-1 FXHO engine in a Duracraft 1648SV, using a Yamaha XL1200 pump (155 mm) and it runs without cavitation issues on relatively calm water. If I get in chop about 1 ft in height, then it starts cavitating like crazy. Or, if I try to go too fast into a corner, it will also catch air. But hey, so will my Merc 50 prop drive on my Triton johnboat. ANY boat will cavitate under the right conditions.

One thing you could try is to install a top-loader intake grate, this will feed more water to your pump to keep it from starving. Also, you could try a wet wolf adjust-a-thrust nozzle cone. The AAT cone has a spring-loaded shuttle that allows more water to flow through the pump at low speeds, and closes up a little at higher speeds, for more thrust pressure, and as such, it can significantly reduce cavitation. 

When you put another person in the boat and it won't take off, is that person in the front, or the rear of the boat? If there's not enough weight on the stern to put the pump low enough in the water, it will cavitate like crazy. 

Try shifting some weight around. On my jetboat, the battery and both fuel tanks are in the stern, and if you look at most jetboats, they try to put as much weight to the rear as possible. If you start to porpoise, you can always install a trim tab, which you can make from a 1/4" X 2" wide strip of aluminum plate, welded to the back end of the ride plate, at a slight downward pitch. That little tab will be enough to take out the porpoising, it's what I did with my boat.

One other thing.....take a look at the hull in front of the intake scoop. Is there a strake located there? If so, this can channel an air pocket along the keel of the boat and into the pump, causing cavitation. If there's a strake, the best thing would be to remove it for at least 2-3 feet in front of the pump (even better, remove the entire length of the waterline and be done with it), then, use a piece of 3/16" X 3" wide aluminum plate, welded, riveted, or bolted flush to the hull of the boat.

Hope this info helps. Keep us posted!


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## willholl79

Thanks for the comments. The fuel tank, battery, etc is in the back. With a 2nd person in the boat, I tried sitting both people in the back and it still wouldn't plane. I am going to try a different grate like you suggested and see if it helps. At first I thought it was "blowing out" because the pump nozzle sits too low in the water, but the more I think about it, I believe the pump is sucking air.

I'll try to post some pictures later today.


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## willholl79

Here are a couple of pictures I already have. I will get some better ones later.



[URL=https://s247.photobucket.com/u...MG_20130603_175231_6791_zps60cf61ae.jpg[/img][/url][URL=https://s247.photobucket.com/u...MG_20130603_180009_1321_zps6c4b7970.jpg[/img][/url]


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## willholl79

And, yes it does have 2 strakes in front of the grate. I will get a picture of the underside of the boat later.


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## PSG-1

[url=https://www.tinboats.net/forum/viewtopic.php?p=318034#p318034 said:


> willholl79 » 1 minute ago[/url]"]And, yes it does have 2 strakes in front of the grate. I will get a picture of the underside of the boat later.




Bingo! This is probably a large part of the issue with cavitation.


BTW, here's a picture of a top-loader grate:




Notice how it has the scoop toward the rear edge like a conventional grate? But it also has that blade farther toward the front. This blade is pitched at a slightly different angle, and it feeds water to the "top" of the pump (the upper radius) which keeps it from sucking air and cavitating. Also, it only has 2 longitudinal tines, which eliminates some of the air pockets that would be created with a multi-tine grate.

Only drawback of the top-loader is that it becomes a vacuum cleaner, and that's not a good thing if you plan on operating in a lot of grass and other debris. Due to the areas I operate in, I had to decide whether I wanted to eliminate cavitation, or be able to keep weeds out of my pump, and I decided to go back to a factory grate, then modified it to be a swing-down "stomp grate" for easy cleaning of weeds.

In your case, I still think the strake may be the culprit. Especially if there's 2 of them!


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## willholl79

The intake is centered side to side in the hull, and the strakes are just to either side, cut off about a foot or so in front of the intake.

The jet ski used was a 1991 Yamaha WR500. I wonder if i can find a direct fit top loader intake grate for that model?


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## willholl79

The strakes actually end a little over 2' in front of the intake.


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## PSG-1

[url=https://www.tinboats.net/forum/viewtopic.php?p=318037#p318037 said:


> willholl79 » Today, 10:16[/url]"]The intake is centered side to side in the hull, and the strakes are just to either side, cut off about a foot or so in front of the intake.
> 
> The jet ski used was a 1991 Yamaha WR500. I wonder if i can find a direct fit top loader intake grate for that model?




Check Riva Yamaha performance parts, you should be able to find a top loader grate for that model. These grates are model specific, and will bolt right on with no modification required.

With the strakes being on either side of the flow path, they may not be the culprit as I initially thought. Especially if they've already been removed a foot or two in front of the intake area. If the strakes were directly in line with the intake, they would definitely cause issues.

That said, you should first try a top loader grate, that's the cheapest, quickest, and simplest variable to experiment with, and I think you'll see some improvement. 

Next variable would be the AAT nozzle cone, and experiment with different shuttle lengths (be careful, though, too long of a shuttle will over-lug a 2 stroke engine, so, follow the instructions carefully)

Another variable to experiment with: the impeller. My guess is that you're probably using a conventional type blade, as that's what most factory impellers are. You could try a Concord (swirl) type impeller, they tend to run better with less cavitation. In my boat, I'm running a 13/19 pitch Solas Concord impeller.


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## willholl79

Here is a picture of the intake:

[URL=https://s247.photobucket.com/u...IMG_20130609_115906_862_zps335879f1.jpg[/img][/url]


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## willholl79

Thanks for all your help PSG-1. I'll order an intake grate as soon as I can find one.


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## PSG-1

It looks like they've got enough of a flat area ahead of the intake that it shouldn't cause cavitation. 

I do notice a livewell plug in the middle, this small protrusion _could_ be enough to cause an issue. Not saying that it is, but it could. Maybe try running it with that plug removed and capped off with something flat, see if it makes a difference. 

If that doesn't do anything, next step would be the top loader grate.


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## willholl79

[url=https://www.tinboats.net/forum/viewtopic.php?p=318064#p318064 said:


> PSG-1 » 09 Jun 2013, 14:44[/url]"]It looks like they've got enough of a flat area ahead of the intake that it shouldn't cause cavitation.
> 
> I do notice a livewell plug in the middle, this small protrusion _could_ be enough to cause an issue. Not saying that it is, but it could. Maybe try running it with that plug removed and capped off with something flat, see if it makes a difference.
> 
> If that doesn't do anything, next step would be the top loader grate.




Good call on the live well plug.


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## PSG-1

I'm thinking it could be that plug. You'd be surprised what a difference something as simple as that can make. Keep us posted.


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## willholl79

I am having a hard time find a top loader intake grate for a 1991 Yamaha WR500. Maybe I can find the part number for the original and see if it fits another ski?


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## willholl79

Well, In calling around I found that the only company that made a top loader grate for the WR500 is no longer in business. I did find pictures of one:
[URL=https://s247.photobucket.com/u...ums/gg138/willholl79/G6_zpsbc0ad789.jpg[/img][/url]

[URL=https://s247.photobucket.com/u...ums/gg138/willholl79/G2_zpsfec3b4e8.jpg[/img][/url]


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## PSG-1

Try to cross reference some similar Yamaha jet skis and see if the part number is the same for the intake grate. If you can find a similar model that uses the same part, you may be able to find a top loader grate for that. 

Typically, a lot of parts are similar for pumps that are similar sized, for instance the GP1200 and XL1200 have parts that are interchangeable, because both pumps are 155mm.


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## willholl79

[url=https://www.tinboats.net/forum/viewtopic.php?p=318218#p318218 said:


> PSG-1 » 10 Jun 2013, 19:04[/url]"]Try to cross reference some similar Yamaha jet skis and see if the part number is the same for the intake grate. If you can find a similar model that uses the same part, you may be able to find a top loader grate for that.
> 
> Typically, a lot of parts are similar for pumps that are similar sized, for instance the GP1200 and XL1200 have parts that are interchangeable, because both pumps are 155mm.






I haven't gone as far as cross referencing part numbers yet, but I called RIVA and Pro Tec and they both told me the best chance is finding a used one, as no one makes them anymore.

I may have to build one based on the pictures above. 

What's the best way to eliminate a worn impeller/wear ring?


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## PSG-1

> I haven't gone as far as cross referencing part numbers yet, but I called RIVA and Pro Tec and they both told me the best chance is finding a used one, as no one makes them anymore.
> 
> I may have to build one based on the pictures above.
> 
> What's the best way to eliminate a worn impeller/wear ring?




Excessive impeller to wear ring clearance will cause loss of top end, overall performance, and guess what else? Cavitation! Generally, acceptable range is .005" to .020" To check, remove the intake grate, and use a feeler guage to take a reading.

If it's excessive, this could be your problem.

On a typical Yamaha jet pump you have 4 parts. The wear ring, the stator, the thrust nozzle and then the steering nozzle. Some models like mine also have a reverse gate. 

This is a breakdown for how to disassemble the XL1200 pump. Yours is probably similar as it's also a Yamaha.

First, remove the ride plate. This will allow access to the pump. Remove the steering nozzle. The remove 2 support bolts for the thrust nozzle. Should also be 2 more bolts that hold the wear ring assembly in place. Remove those. Then, remove the 4 long bolts that go through the pump assembly, located on the 4 corners of the thrust nozzle flange. Tap on the thrust nozzle with a rubber mallet, and wiggle it, then remove it. Now, disconnect the cooling line from the stator assembly by loosening the hose clamp. 

For the stator, you'll need to use a pry bar, and pry at the designated points (small tabs on either side of the components where they mate together) The stator assembly should slide back when you pry. Once you get it to move back, then, you'll need to remove the engine coupler from the driveshaft, so you can slide the shaft out through the hull with the stator unit.

After removing the stator, then you can remove the wear ring assembly. Same procedure, use a small pry bar on the tabs, and carefully alternate from left side to right side, so as not to break the tabs.

Once you have the old wear ring assembly removed, install the new one, and re-assemble pump in reverse order. PAY PARTICULAR ATTENTION TO THE ALIGNMENT PINS THAT GO BETWEEN COMPONENTS, they are easily lost! Be sure pins are in place before assembling the components.


As for your impeller, you will need 2 BFW's (large wrenches) :mrgreen: Place one BFW on the flats of the shaft. Place the other on the nut of the impeller. (If impeller has no visible nut, but a rubber bushing, pry out the bushing. You will need a specialized impeller removal tool to remove a splined-face impeller) To remove the impeller, remember it is a LEFT-HAND THREAD, so, turn right to loosen.

You can have a worn impeller re-built by a company called Impros. They can also re-pitch it to whatever pitch you want.


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## willholl79

Thanks again for the help PSG-1.


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## PSG-1

Not a problem, glad to be of assistance. Keep us posted on what you find out.


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## willholl79

I found this grate on ebay that should fit. I wonder if it will be an improvement over stock?

[URL=https://s247.photobucket.com/u...EE-kN7fOBP8Y0VeZyw60_57_zps65b5b3b7.jpg[/img][/url]


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## PSG-1

Perhaps so, because it has fewer tines, and the angle of the blade is probably more aggressive than a stock grate. You could also make a piece of plate and put it about halfway, then weld it at a forward-facing angle. Pump components such as grates, etc are cast aluminum, and generally weld without difficulty, so, they're easy to modify.


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## willholl79

I'm going to try that grate and may add to it depending on results.

I took the intake grate off to check the impeller and wear ring. It looked suprisingly good. Some very minor pitting on the impeller blades but no nicks or gashes. Wear ring shows no scoring. I didn't have a feeler guage on hand(my tools are still packed up form moving 2 months ago) but it looked tight. I was kind of dissappointed that it wasn't trashed and the main problem.

If it's not sucking air through the intake grate, then it's got to be "pushing out"because of the nozzle being too shallow.

The first and only tme I've had it in the water it ran better with just me in the back as opposed to 2 people in the back. We had it weighted down to the point water was flowing over the transom when decelarating. 

Even with just me on the back and on plane, it didn't run level like a jet boat should. The previous owner has it set up to drive from the rear, but to run level on plane the driver needs to set over the motor.


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## PSG-1

> If it's not sucking air through the intake grate, then it's got to be "pushing out"because of the nozzle being too shallow.
> 
> The first and only tme I've had it in the water it ran better with just me in the back as opposed to 2 people in the back. We had it weighted down to the point water was flowing over the transom when decelarating.
> 
> Even with just me on the back and on plane, it didn't run level like a jet boat should. The previous owner has it set up to drive from the rear, but to run level on plane the driver needs to set over the motor.




Based on that, it could be that there's actually too much weight on the stern, which could put the forward edge of your intake scoop near the aerated water being created as your boat moves along slowly before you try planing off. Then when you try to plane off, it sucks all that aerated water and causes it to cavitate. 

Maybe try shifting some weight forward and see if that changes it. This should put more of the hull in contact with the water, and hopefully give the water running along your keel enough distance to smooth out before hitting the pump intake. 

Top loader grate will also help with this, as well.


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## RivrLivn

I'm definitely no jet-jon expert, but from the pic the whole bottom of the boat especially the transition from one hull to the other in front of the intake looks extremely rough. I know my boat has a very smooth delta pad that runs 8 feet out to create a smooth feed to the intake. I have heard of people just having a small dent in front of the intake causing performance issues. 

Just a thought. Looks like a fun little project when you get it running good.


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## PSG-1

You may be right about that, RivrLivn. Good call.

From the photo, it's hard to tell if the strakes are on either side of the intake scoop, or if they're right on the edges. If they're too close to the edges, it would indeed cause a massive air pocket, and cavitation. Hard to tell without being there to see it in person and lay a straight edge on those strakes to see if they miss the intake area.


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## willholl79

You are right Rivrlivn, the transition leaves a lot to be desired. It is definitely on the list of things to address. 

I'm going to try a few things to try to make it run better, without putting tons of time and money into it, not knowing if it will do what I need; taking 2 people and gear up and down the river.

According to my research, the WR500 Waverunner weighs in the neighborhood of 400Lbs.
A Sylvan 1436 weighs 175Lbs empty. Take the motor/pump at a guesstimated 200Lbs and add it to the the jon you get 375Lbs. I understand you have to account for the more surface area on the flat bottom jon and such, but hillbilly math says the 500cc(with oversized pistons and carb) should haul a couple people up and down the river assuming it's not "sucking air" through the grate or "blowing out" the back.


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## willholl79

[url=https://www.tinboats.net/forum/viewtopic.php?p=318530#p318530 said:


> PSG-1 » 12 Jun 2013, 18:40[/url]"]You may be right about that, RivrLivn. Good call.
> 
> From the photo, it's hard to tell if the strakes are on either side of the intake scoop, or if they're right on the edges. If they're too close to the edges, it would indeed cause a massive air pocket, and cavitation. Hard to tell without being there to see it in person and lay a straight edge on those strakes to see if they miss the intake area.




The strakes are just to the edge of the intake, maybe an inch or so outside of either side.(the grate is not in)

[URL=https://s247.photobucket.com/u...IMG_20130612_192329_874_zpscbd881d1.jpg[/img][/url]


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## PSG-1

That's a better angle on that photo. 

Looking at it, I can clearly see the strakes are definitely to the sides. I wouldn't think that would cause problems, but then again, I may be wrong.


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## willholl79

Update: The used pro-tech intake grate got here yesterday and I put it on this morning, put the livewell plug in so that nothing was sticking below the hull and put it in the water. Much, much, better! Not perfect, but it's improving. It now planes and runs WOT with 2 people. It likes smooth water, the least little chop and it hesitates a little, but I think I can work that out.


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## PSG-1

Glad to hear it's working a little better. As for cavitation in chop, no way to completely get rid of that problem. 

I just got back from the Santee Delta today. The tide was falling, and the wind blowing from an easterly direction, so, there were a few places it was choppy and I simply had to back it down and go slow. My boat likes flat water, but if I start getting in chop 1/2-1 ft in height, it starts cavitating like crazy. But even an actual jetboat will have this problem. I know, because I used to own a 14 ft Sea Doo Speedster, it didn't like chop, either.


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## willholl79

When I had the boat in the water this morning, it ran decent in smooth water; almost glass. The slightest ripple from the wind would cause some cavitation.

Edit: This was with me, my wife, and 3 year old son in the boat. I didn't get a chance to run solo.


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## willholl79

My next question: If I were to upgrade the prop, what pitch would give me a little more low end(plane quicker), and not kill the top speed?


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## PSG-1

Now THAT is a difficult question. :? What pitch is the impeller you're using?

In my boat, I'm running a 13/19 pitch. Also had good results with a 14.5/17 pitch

Unlike a boat prop, which is the same pitch, jet boat impellers are progressive pitch, meaning the leading edge has a steeper pitch to pull the water in quickly, this is where the hole shot comes from....and then changing to a higher final pitch at the trailing edge, where the top end is generated.

Lower pitch can handle aeration/cavitation better than higher pitch. In your case, I'm thinking a 13/19, or maybe even a 12/18 would have better hookup in chop, without losing much top end.

Impros can re-pitch your prop to whatever pitch you want. Check out their website, they have a good bit of info about props.


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## willholl79

[url=https://www.tinboats.net/forum/viewtopic.php?p=319162#p319162 said:


> PSG-1 » 17 Jun 2013, 17:28[/url]"]Now THAT is a difficult question. :? What pitch is the impeller you're using?
> 
> In my boat, I'm running a 13/19 pitch. Also had good results with a 14.5/17 pitch
> 
> Unlike a boat prop, which is the same pitch, jet boat impellers are progressive pitch, meaning the leading edge has a steeper pitch to pull the water in quickly, this is where the hole shot comes from....and then changing to a higher final pitch at the trailing edge, where the top end is generated.
> 
> Lower pitch can handle aeration/cavitation better than higher pitch. In your case, I'm thinking a 13/19, or maybe even a 12/18 would have better hookup in chop, without losing much top end.
> 
> Impros can re-pitch your prop to whatever pitch you want. Check out their website, they have a good bit of info about props.



The stock impeller for a WR500 is an aluminum 16 pitch(average of 15/17????), according to the interwebs. When I looked at the impeller through the intake grate, it is aluminum, I assume OEM.


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## PSG-1

If it's aluminum, it's definitely stock! 

And you should definitely replace it with a stainless impeller. A swirl-type, such as a solas concord, or a skat-trak, would probably make a noticeable difference in the overall performance.

If your prop is a 15/17 pitch, you'd probably have the best results by stepping down to a 13/19. It will give a little more top end (maybe .5 - 1MPH) but the lower pitch of the leading edge should give it a better bite in the water, and reduce the cavitation.

Here's some tech info, as well as a link to Impros:

https://impros.com/store/index.php/tech-info/tech-q-a.html


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## willholl79

Solas stocks a 13/18 and a 14/18. I'm thinking 13/18 due to weight.


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## PSG-1

13/18 would probably be best, due to weight and the existing problems with cavitation. 

Reading through the tech info, it says that aluminum impellers use a larger hub, which does not allow as much water to flow through the pump as using a smaller hub, like they do with stainless. 

Also, while you have the pump apart, check your stator vanes for chips, nicks, etc. If the vanes are damaged, that can also cause cavitation.


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## willholl79

Ordering the 13/18. We'll see what happens!


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## willholl79

Update: After fabing up a hood and dressing up the boat a bit on Sat. I took the jet jon out solo this morning. I put in just after daylight, the water was like glass and the boat ran awesome. I fished for 3-4 hours and headed back down river. There was a slight breeze and the ripples in the water caused cavitation like crazy, barely able to hold it on plane on the way back down to the ramp. I loaded up and headed home a little excited about the performance on smooth water, but wondering what I was going to do about the fixing cavitation in the light ripples. I got home and decided to go ahead and install the Solas prop that came in the mail yesterday. When taking the pump apart I noticed there was a good sized chunk(half dollar size) missing from the trailing edge of one blade on the stock impeller. I guess I couldn't see it from the intake. I'm hopefull this will solve my problems. The drive cone had all three ears broken when I pulled it apart, so I have to wait a few days for parts to get her back going but I expect good things.


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## PSG-1

The half dollar sized chunk missing from the prop is definitely the culprit! You should notice a DRAMATIC improvement in performance after installing the solas prop.

When you say 'drive cone' are you referring to the cone on the back end of the stator? If those mounting bolt ears are busted, when you pull that cone to replace it, you need to check to see if water infiltrated the bearings. If so, you'll need to change those out. If not, then, be sure to replace the O-ring when you replace the stator cone.

Also, as I mentioned before, be sure to check the stator vanes for damage, in case that missing chunk of impeller shot through and hit something.


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## willholl79

Here's a picture of the missing chunk:

[URL=https://s247.photobucket.com/u...IMG_20130624_183035_999_zps054f2831.jpg[/img][/url]

Old/new:

[URL=https://s247.photobucket.com/u...IMG_20130624_182958_867_zpsfbd2383c.jpg[/img][/url]


I also made a hood and folding bench seat:

[URL=https://s247.photobucket.com/u...IMG_20130622_191336_901_zpsaa29815e.jpg[/img][/url]


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## willholl79

[url=https://www.tinboats.net/forum/viewtopic.php?p=319908#p319908 said:


> PSG-1 » 23 Jun 2013, 20:02[/url]"]The half dollar sized chunk missing from the prop is definitely the culprit! You should notice a DRAMATIC improvement in performance after installing the solas prop.
> 
> When you say 'drive cone' are you referring to the cone on the back end of the stator? If those mounting bolt ears are busted, when you pull that cone to replace it, you need to check to see if water infiltrated the bearings. If so, you'll need to change those out. If not, then, be sure to replace the O-ring when you replace the stator cone.
> 
> Also, as I mentioned before, be sure to check the stator vanes for damage, in case that missing chunk of impeller shot through and hit something.




The drive cone is full of grease, and there's very little evidence of water intrusion. The bearings look and feel great. The stator vanes do show a bit of wear, I'll probably replace that also.


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## PSG-1

[url=https://www.tinboats.net/forum/viewtopic.php?p=320060#p320060 said:


> willholl79 » Today, 18:59[/url]"]Here's a picture of the missing chunk:
> 
> [URL=https://s247.photobucket.com/u...IMG_20130624_183035_999_zps054f2831.jpg[/img][/url]




YIKES! Yep, that would definitely cause cavitation. I think you will see a noticeable difference when you install that new, undamaged prop.




> Old/new:
> 
> [URL=https://s247.photobucket.com/u...IMG_20130624_182958_867_zpsfbd2383c.jpg[/img][/url]




Note how the hub of the stock prop has that extension with the wrench flats. Those can cause cavitation. The newer impellers have recessed splines, and use a specialized tool to install with (they should have sent you one) and it's capped with a rubber or aluminum grommet. This gives the water a smoother path to flow across.





> I also made a hood and folding bench seat:
> 
> [URL=https://s247.photobucket.com/u...IMG_20130622_191336_901_zpsaa29815e.jpg[/img][/url]




Very nice! Did you install any sound proof foam in the cowling? If not, you should consider doing that. Mcmaster-Carr has some that reduces sound by up to 80% and it is fire retardant. Installing the egg crate acoustic foam will dramatically reduce engine noise, making your ride more quiet.


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## willholl79

No sound proofing yet, but it's on the list.


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## PSG-1

Roger that. 

From my own personal experience.....use the egg crate foam instead of dyno mat, it's much lighter, and does the job better, too. I tried both, and was much happier with the egg crate foam.


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## Ranchero50

You need a spoon in front of the pump inlet. It pushes the air that is trapped by the strakes outboard and hydrodynamically sucks the water up to the pump. Makes all the difference in the world for cavitation and is the bane of jet jons.

Check out my build thread.


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## PSG-1

Ranchero is absolutely right, a spoon helps take out a lot of cavitation. Look at any jet ski or jetboat, they're all designed like that. 

I went back and looked at how you did your spoon modification, Ranchero, and it looks like a fairly easy modification that can be made to an existing hull. And you said it made a big difference in your boat's performance. So, now I'm thinking maybe at some point I should do this with my boat, it sure would be nice to be able to run in chop without all that cavitation.


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## willholl79

I finally got it buttoned up from the impeller swap. Took it out yesterday with my wife and son. Zero cavitation issues. With 2 people, the boat maxed out at 22 mph down stream. Took it out today solo and zero cavitaion with a max of 25 mph down stream. The boat runs great! I am already wanting more room and more power. A 1656 that runs 30-35 would be ideal.


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## PSG-1

Outstanding! Glad to hear you got the issue resolved with the cavitation. =D> I was hoping the new impeller would make a difference.


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## willholl79

[url=https://www.tinboats.net/forum/viewtopic.php?p=320668#p320668 said:


> PSG-1 » 30 Jun 2013, 17:12[/url]"]Outstanding! Glad to hear you got the issue resolved with the cavitation. =D> I was hoping the new impeller would make a difference.



Thanks for all of your help! I think I lost a few mph with the new impeller, as I bought it assuming my stock impeller wasn't fubared and I had a cavitation problem, but the hole shot is great and there is no cavitation. I could probably play with the impeller pitch and get a few more mph, but for what it is, I'm going to give it hell and see how long the motor holds. Today I ran it up river probably 10-12 miles at 3/4 to wide open throttle. No issues.


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## PSG-1

Man, that's great! As I said before, if you decide to play with impeller pitch, you can always have your prop re-pitched by Impros.

As far as the motor, 2 stroke PWC engines can run for anywhere from 200-1000 hours before they have to be re-built, it all depends on how well they are taken care of. 

Having ridden jet skis for the last 25 years, I can tell you that the biggest 2 causes of failures on 2 stroke PWC's are a lean condition causing piston siezure or failure....and water ingestion into the engine, which is more common on PWC's than in boats, unless you get swamped. That, and letting them sit too long without turning them over, and the insides get rusted then the piston starts scoring the cylinder walls, causing failure.

That said, if/when your engine ever does take a crap on you, send it to SBT, they can re-build a 500cc engine for around 700 dollars. I had a 750 Kawasaki engine rebuilt for about 900 dollars when I siezed it doing a submarine with my jet ski, and I had a couple of Tigershark engines re-built by them.

You can opt for the standard re-build, and it's a little cheaper, but I suggest spending the extra money, which gives you a 2 year no-fault warranty. Regardless of the cause of engine failure, they will re-build it for free! That's a helluva deal.


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## willholl79

If/when the 500cc takes a dump, I'll probably swap in a 650cc. From what little research I've done, it will bolt up to the motor mounts and driveshaft. I'm not sure about electronics and carb., but the extra power without much weight added would be nice.


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## PSG-1

My first jet ski was a kawasaki 550, way back in 1986. Rode 550's for years, until going to a 750 around the year 2000, then finally going to the Yamaha Super Jet about 5 years ago. The 550's and even the 750 were great engines, but the hulls could never withstand the abuse I gave them, lots of broken handle poles and nose cones (gee, maybe that has something to do with my sciatica...LOL)

Anyhow, I never actually looked at the 550 and 650 to see if the motor mounting plate had the same hole pattern, but the 2 engines are very similar in size, so it's possible. 

The Tigershark 900 and 1000 had the same bolt pattern, in fact, those 2 engines used the same parts, except for the CDI and the carbs. So, it may be the same deal with the 550 and 650. You might be able to find out on the PWCtoday forum.


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