Jet Boat cavitates on takeoff

[RandyJ]

I posted this a couple of nights ago and never got a reply... so here it is again.<br /><br />I've got a 1992 Waverunner 650 VXR. Yep guys, I bit the dust and got me a scooter for the days when the fish ain't biting. So, cool your jabs... I'm an old fart who still likes to have fun. PROBLEM... when I take off it tends to cavitate then grab some traction and take off... Anyone know what causes this or what to look for. This is my first PWC/scooter... and I would like for it to operate correctly.<br />Yeah I know this is an outboard site but somebody ought to know something and there is no good PWC site to repair these things.

 

[Yepblaze]

Re: Jet Boat cavitates on takeoff

Maybe it's supposed to be that way. Seems to me a 650 with a jet would need all the help it could get to get up to speed, and the raised RPMs may be normal.

 

[Forktail]

Re: Jet Boat cavitates on takeoff

This isn't uncommon for a PWC. There are aftermarket impellers and intake grates that can solve this problem. If you're looking for holeshot, you may need a lower pitch impeller. Try www.overtons.com<br /><br />The reason it's cavitating (ventilating), is that the PWC's fast turning impeller needs more water supplied to it than is available. This causes a pressure change on the impeller and thus ventilation. That's why it feels like it's losing "grab". The weight of the PWC, with you on it, and the fact it can't move forward quick enough to supply fresh water to the intake and impeller causes this.

 

[RandyJ]

Re: Jet Boat cavitates on takeoff

Thanks guys.... I've taken to the PWC's, specifically Yamaha waverunners this summer and ended up with 4 of them. The others are 500 and a 650 waverunner III. Neither of them cavitate. I don't doubt that design is part of the problem since it seems that with a passenger the ski does not seem to cavitate. I thought maybe someone would know something about adjusting the ride plate or some other suggestion which would change the trim to alleviate cavitation. If it were happening all the time I would think it was the impeller. If it were happening on turns I would think it were trim. But since it is only happening on hole shot I'm confused.

 

[sho305]

Re: Jet Boat cavitates on takeoff

Some of them have a plastic sleeve around the impeller that gets worn from sand, then you loose some clearance to the impeller. Some are set up to go faster with less intake scoop, they are harder to get bite out of the hole. I was told to ease onto the gas until moving a little, then go. That way the water gets moving through the jet before full power. Also any weed/weeds in there will hose it up.

 

[sloopy]

Re: Jet Boat cavitates on takeoff

Is the intake cloged with leaves or other stuff we don;t want to know about?? that cuases it on my FX 140 Fourstroke by Yamiha I also got this neat little sailboat that I love it never Cavitates