Jet jon cavitation issues

[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.

 

[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.

 

[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]

 

[willholl79]

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.

 

[PSG-1]

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.

 

[willholl79]

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

 

[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.

 

[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.

 

[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.

 

[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.

 

[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.

 

[willholl79]

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.

 

[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.

 

[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.

 

[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.