Custom/Hybrid Rickter XFS cavitation issues

[Polish jet pilot]

The same 727 cc motor and pump in my "light" SJ had no cavitation issues at all. Now, in the XFS Current prop is skat 12/17, (i have the oem big hub 2008 - 3mm to try) and it cavitates badly atimes. No its not damaged and pump has FS cone and bored nozzle to 85mm - what do you think? Its strange the other rickter that came ad now has our 845cc with oem pump and 14.8/18 prop cavitates like crazy once it starts cavitating... so same problem as with the 727cc ski - can anybody propose a solution - XFS users out there?

Thanks for all hints

 

[BruceSki]

a freestyle cone and a bored nozzle dont work well together unless you are running a giant prop.

Pick one the cone or the 85mm nozzle and try it again.

 

[Polish jet pilot]

It worked quite well in the SJ...that's why I'm stoked...I put everything in rickter and it cavitates

 

[BruceSki]

maybe it was a slight unnoticed issue in the heavier boat, and the lighter boat magnified it?

 

[Polish jet pilot]

thats what I was assuming, so change prop and go?

 

[Polish jet pilot]

and no no cavitation issues before...it must be the shape of ski /weight thing...maybe oem motor and oem pump work just fine in xfs but with tuned components this lightness becomes evident..??

 

[BruceSki]

I would try a larger pitched prop, or a stock sized nozzle or a stock tailcone.

Do one at a time and see how it performs. This becomes trial and error with a hull with a different bottom deck and much lighter than the previous hull.

You will have to "test and tune" until you get it dialed in.

 

[DangerBoy]

make sure your midshaft housing is sealed to the firewall
Db

 

[Polish jet pilot]

Thanks DB, btw your couplers work so well. I will check the seal too.

 

[Polish jet pilot]

Bruce I agree will play with the pump - maybe a new pump seal would be also a good thing...

 

[BruceSki]

Pump seal can't hurt. That's a cheap part anyhow

 

[waterfreak]

Pump seal can't hurt. That's a cheap part anyhow

yes, a new pump seal is a "must" when assembling a new hull!

 

[Polish jet pilot]

I wanted to be economical, but it seems there is no easy way The seal looked OK, but is 10 years old...

 

[Matt_E]

A new pump seal costs less than $25. Not the place to be economical.
That said, the old seal would have to have very visible flaws for it to cause the issues you're describing.

 

[Polish jet pilot]

that is why i did not change it - looked normal...maybe need to work with pump to hull tolerances... or maybe its the hull itself - just way lighter in handling than oem SJ and prop is spinning ...

 

[Polish jet pilot]

I also think the oem 2008 -3mm prop will be much better for hookup as its big hub type...

 

[Matt_E]

I'm having a hard time with that weight thing you're postulating.
When I put my drivetrain from my Superjet into my carbon Freak (about 100 lbs lighter, you're nowhere near that difference), I used the old seal and changed the impeller pitch from a 13/17 to a 14/17. That's it, no other change. Guess what, no cavitation whatsoever.
(This is a mag pump, though)

 

[BruceSki]

Try a stock tail cone first. That's free and takes all of 30 seconds.

 

[superramjet]

The ride plate is very short, silicone the gap between the front of the ride plate and rear of intake grate, I'm pretty sure it pulls air from the ride plate cavity. Mine had an easy 1/4" gap. The o8 sj prop won't be enough for ur engine if it's tuned right. The intake area is much bigger than an sj too, u can't expect same prop/nozzle combo that worked in sj to transfer exactly to xfs hull, I had to prop up a little

 

[Polish jet pilot]

good info superramjet, I did install everything just to get it to water, and did not use any silicone anywhere - I will check all the gaps - this cant be a big problem, just fine tuning the package... one way or the other the ski is pretty amazing... as regards to SJ 2008+ prop its taller on the bottom as it is 13/16 and my skat is 12/17 - not sure whether I am comparing apples to apples as the props differ greatly - will swap and compare once I get the time to do it..