Cavitation

[cyclone]

My boat cavitates horribly out of the hole. I can only take off at half throttle. If I punch the gas peddle, I go almost nowhere and the motor will rev like crazy. What would cause this and what is the fix?

[miller19j]

I would take a look inside your pump and make sure that you don’t have any foreign objects stuck in there. Then check the o-ring on the hand hole to make sure it is sealing. If you find nothing there check that the main Bowl bolts are tight.
If the above looks OK. It sounds like you need to rebuild your jet. What kind of power does your boat have?
[ December 02, 2002, 10:33 AM: Message edited by: miller19j ]

[cyclone]

i'm pretty sure there is nothing stuck in the jet. The pump was supposedly rebuilt but it's questionable.
I've got a BBC making about 500hp.
Another thing i've noticed is that i'f I'm cruising at 3,000rpm and punch it, the motor revs quite a bit before the boat goes any faster. I think the pump is probably wore out. The pump stays loaded through the chop, but out of the hole it really sucks.

[miller19j]

My guess is that you need to rebuild you pump. But I am no expert maybe someone else will chime in here.

[Blown 472]

Sounds like a loose pump to me.

[MikeF]

Cyclone,
Probably a loooooose pump.
Whenever you give it any go pedal it should move forward as soon as you step on it. When it does not move forward, pressure is being lost somwhere.
As far as jumping on it for the holeshot, You might always have to feather the throttle anyway. Until the boat starts moving forward and supplying the intake w/ more water you will probably have some type of "lack of water" problem. I do not have any experience w/ the Inducer impeller some say that it works very well.
I'd say w/ the power that you are moving up to (is that still the plan?), you will probably need it (inducer)!
http://free.***boat.net/gallery/Reader_Rides/Jet_Boats/Cyclone5K.JPG
http://free.***boat.net/gallery/Reader_Rides/Jet_Boats/Cyclonescoop.JPG

[cyclone]

Hey Mike do you have any other pics of my boat? And what does the inducer do? The reason i thought the cavitation out of the hole was odd is because my old boat didn't do it. I could put my foot right to the floor and the boat would just take off. And yes, the plan is still the same.

[miller19j]

The inducer is a device that looks a lot like a propeller that goes on the shaft just in front of the impeller.
This is a pic of one from froggys thread
http://www.highperformancecars.com/froggystyle/pump_mods1.jpg

[cyclone]

thanks for the pics. What does it do though?

[058]

NEWS FLASH.....jetters have props eek! eek! eek! :D :D :D

[miller19j]

cyclone:
thanks for the pics. What does it do though?It helps load the impeller. It is foreword on the shaft inside the suction piece. It acts like an active loader supplying more water to the impeller. There is a website that has more info but I don’t know where it is. Maybe someone will chime in with it.

[Oldsquirt]

058:
NEWS FLASH.....jetters have props eek! eek! eek! :D :D :D Sorry Bob, that's still not a prop :D In fact it is very similar to a jet ski impeller eek!
Cyclone, for more info on the inducer Don's Pump Service (http://www.donspumpservice.com/pubhtml/jetdrive.htm)

[Boater Bill]

Cyclone-if you have your pump gone thru spend the xtra coin and get the inducer. It does help with holeshot and cruise rpm's. I had one installed. My hp is around the same as yours now and I can still induce cavitation when I mash it from idle so you will need to feather the throttle as MikeF says.

[cyclone]

Hey Bill what did jack charge you for all your pump work and to have the inducer installed? I think i read somewhere that you have him do yours.

[flat broke]

Froggy,
Why the .040 clearance on the wear ring. Thats a little on the loose side. I know you boat down in the lower river area, but even with the sand and silt suspended in the water, isn't that a little loose? Not stirring up shit, just wondering why you chose that clearance.
Mike(Cyclone),
Give Jack a call 949-631-2040. He'd be more than happy to talk to you about your setup. I don't know exactly how much HP you are planning on for the next motor, but the DPS inducer might not be needed in your application. There are other things that can be done asside from the DPS inducer that can help with cavitation. Right now I think your cavitation is a symptom of a worn pump and not a trait I would immediately step up and buy the DPS inducer to rectify. Give Jack a call; one of the many reasons I like him is that he wont try and sell you something that you don't need.
Good luck,
Chris
[ December 03, 2002, 09:22 AM: Message edited by: flat broke ]

[cyclone]

so is the inducer strictly a hole-shot item or does it help across the board?

[HBjet]

Hole-shot! A tight pump will help you with acceleration after your on plane. Like mashing the gas at 3k rpm.
Before you do all this pump work, I would like into that oil pressure loss problem first!
HBjet

[cyclone]

that problem has been taken care of.

[Froggystyle]

flat broke:
Froggy,
Why the .040 clearance on the wear ring. Thats a little on the loose side. That's funny how everyone thinks that .040 is loose. That is really pretty tight. Stock was .070ish, and I ran from .070 all the way down to .005 in a couple of iterations, and noticed exactly zero performance difference between the various gap measurements. Top speed was the same, holeshot issues were the same, no difference whatsoever except that at .020 and lower there was a marked increase in sand damage to the wear ring and impellers. At .040 and up it was minimized big time. I only ran it as tight as .040 because it set up at that without a shim, so what the hell... Otherwise, I would have probably run it around .050 or .060.
When we opted to do the new Magbronze impeller with the DPS, I wanted to keep the whole thing very serviceable. I also didn't want to sand-damage the impeller in the low river. That was why we went "loose" on the clearance.
BTW, I have seen clearances that worked great all the way up to .120 with no dramas whatsoever. A "good tight pump" is an excellent way for pump builders to ensure work in the future. .040 certainly doesn't decrease performance (on a non-full race setup) and increases component life by a lot.

[miller19j]

Froggystyle:
flat broke:
Froggy,
Why the .040 clearance on the wear ring. Thats a little on the loose side. That's funny how everyone thinks that .040 is loose. That is really pretty tight. Stock was .070ish, and I ran from .070 all the way down to .005 in a couple of iterations, and noticed exactly zero performance difference between the various gap measurements. Top speed was the same, holeshot issues were the same, no difference whatsoever except that at .020 and lower there was a marked increase in sand damage to the wear ring and impellers. At .040 and up it was minimized big time. I only ran it as tight as .040 because it set up at that without a shim, so what the hell... Otherwise, I would have probably run it around .050 or .060.
When we opted to do the new Magbronze impeller with the DPS, I wanted to keep the whole thing very serviceable. I also didn't want to sand-damage the impeller in the low river. That was why we went "loose" on the clearance.
BTW, I have seen clearances that worked great all the way up to .120 with no dramas whatsoever. A "good tight pump" is an excellent way for pump builders to ensure work in the future. .040 certainly doesn't decrease performance (on a non-full race setup) and increases component life by a lot.Froggy I don’t mean to start another controversy but according to the rebuilding manuals that I have it should be set between .025 and .030 for the front clearance. According to them if it is set larger it could allow foreign matter to enter between the impeller and wear ring and cause damage. My wear ring to impeller clearance is .030 so if I set the front clearance to .040 it could potentially allow debris to get wedged between the wear ring and the impeller.
Just some food for thought
By the way if I assembled mine the way the parts came from Berkeley it would have been .150
eek!

[Blown 472]

I had a cavity once.

[flat broke]

Thanks for the response Froggy. I see where you're comming from especially if you've run looser setups with equal results. I figgured with all of the loading problems you were having, you would have been running as tight of a setup as possible while keeping silt/sand damage to a minimum. Thanks for explaining your choice.
Chris

[RiverDave2]

Cyclone, let me know if you need one of those pre impellers installed for you. :)
RD

[HBjet]

RiverDave2:
Cyclone, let me know if you need one of those pre impellers installed for you. :)
RDHoly Shit that's funny!

[cyclone]

im pretty funny. ask anyone.

[roostwear]

Wanna see a REAL loose pump? Unfortunately, it's mine........
http://www.banderlog.com/dcforum/DCForumID1/2004.html

[cyclone]

when jack took the Cyclone's 12JB pump apart he remarked at how good the impeller looked after 31 years of service with zero work done to it. Then he turned the impeller over to look at the other side of it only to find that it was cracked almost all the way around. that was an expensive day.

[GasTurbine]

miller19j:
cyclone:
thanks for the pics. What does it do though?It helps load the impeller. It is foreword on the shaft inside the suction piece. It acts like an active loader supplying more water to the impeller. There is a website that has more info but I don’t know where it is. Maybe someone will chime in with it.My local friend Don Bowers...
http://www.donspumpservice.com/pubhtml/jetdrive.htm