787 water regulator operation and fixing a leak

[2x2smoke]

I'm trying to understand how the regulator works because mine leaks quite a bit.

The inlet from the jet pump diverts water into the water box at all times.

at low engine speed, the water pressure is low so the bellows is empty and the spring in the cap holds the needle valve above the inlet open. This allows water to flow up the secondary tube to the tuned pipe, keeping it cool.

As engine speed increases, water pressure at the inlet inflates the bellows until it overcomes the cap spring tension. It pulls the needle valve upwards, shutting off flow to the tuned pipe. I guess the pipe doesn't need extra cooling at higher engine speeds

My regulator was leaking around the plastic "feeding block" above the needle valve. There is a handy groove on the top of that piece into which I installed an oring which sealed and fixed the water flowing past that area. I think this is copacetic assuming the block body isn't designed to move. (The bellows still moves independently to the block)

an old thread lists info in conflict with how I understand how the thing works: racerxxx

"Water fills the bellows and that(water pressure) and the spring work together to regulate the water flow. The water enters the ski from the pump (13mm line) and goes to a T where a smaller line enters the bottom port of the WCV and the 13mm line goes to the inlet on the head cover. The slide piston in the WVC is gated to allow water to enter the center of the piston through two holes and fill the inside of the bellow and also the water box VIA the taper of the pin. At low RPM the hold down spring in the WCV is stronger than the inlet pressure thus pushing the cap down breaking the seal against the taper of the metal pin to the ID of the metal washer on the under side of the slide piston. This allows more of the water to spray into the water box thru the slot in the tip of the pin and the calibrated fitting that threads into the water box. As RPM's increase the gap between the taper and washer reduce cutting the water flow to the water box by filling the bellow more internally and over coming the hold down spring. At the same time the slide piston is pushed up (by filling the bellow) the 2 holes mentioned earlier now "reach" the upper fitting (outlet) on the WCV housing and inject the water into the head pipe internally to help cool the hot exhaust. This upper fitting is always getting a small amount of water, it just jets more at a higher RPM and the water box gets less. The slide piston should sorta click in to the housing, if not it will probably leak a little and that can be see by riding with the seat off, but you'll need to be at a higher RPM."

He calls the feeding block a slide piston. Does it actually slide?

 

[soccerdad]

No, it does not slide. Per the seadoo shop manual: (download one, they can be easily found for free). At low speeds, more water goes to the pipe. At higher speeds, less. So Racer's description is backwards per the manual. The manual has a good description of the system. I just replaced one of mine due to the leak you described. The valve does need to kind of snap in like Racer said. And I use a small zip tie to hold the bottom of the bellows in place. Mine leaked there. But you need to round off the zip tie and make sure it cannot puncture the bellows over time when it inflates.

 

[2x2smoke]

Thanks.

Lake tested the o ring fix and it seems to have worked to stop the leak there.

Water injected into the tuned pipe interferes (physically or thermal) with the exhaust pressure waves? More water injected at lower rpms make the engine think the expansion chamber is smaller (or colder) to give more low end or mid range power? Then at high rpms, the water injection diminishes to take full effect of the large (or hot) expansion chamber characteristics?

all an elaborate scheme to smooth out the "power band"?

 

[soccerdad]

Thanks.

Lake tested the o ring fix and it seems to have worked to stop the leak there.

Water injected into the tuned pipe interferes (physically or thermal) with the exhaust pressure waves? More water injected at lower rpms make the engine think the expansion chamber is smaller (or colder) to give more low end or mid range power? Then at high rpms, the water injection diminishes to take full effect of the large (or hot) expansion chamber characteristics?

all an elaborate scheme to smooth out the "power band"?

Yes, I think you have it correct. I think it makes it act like a smaller pipe for more low end, then allows the high end of the larger pipe. I think the water causes the gas to contract (spray condensation), thus creating a lower pressure area in the pipe, thus pulling more out of (or into) the motor. Kind of like reverse turbo charging. (sucking instead of blowing) That is what a normal dry expansion chamber does at high end on a two stroke. (along with packing the charge back on the reverse wave) But the water injection helps it work at the lower rpm. But if the regulator is not working, then it will dump too much water into the pipe at high RPM and mess with the balance. NOTE: This is my theory. I have studied two strokes a lot, and tested a lot. But I don't have real test experience with the water systems before my 787 skis. So please don't blast me if I am wrong. Two strokes are cool.

 

[squad1]

The WV on my 787 doesn't appear to be leaking any water, but it is able rotate a bit on the brass fitting on the resonator. My question is, if it is functioning properly should water still be coming out of the rear pisser from the tuned pipe hose when moving? If I read the posts correctly, it shuts off flow to the tuned pipe. Should I not see any water at speed or is it just reduced? Thanks

 

[soccerdad]

They are two separate things. Water for the pisser comes from the cooling loop that goes in the pipe water jacket and not into the exhaust stream. It is a different loop then the water coming from the regulator which sprays water into the exhaust. So you should always have water coming from the pisser. The manual has a great diagram of it. You can DL them for free on the web.

 

[squad1]

Thanks.
I have the manual, but someone in another thread had made mention of a situation where the WV was malfunctioning and an indicator was the water stream underway. Perhaps I miss read/interpreted it.. just wanted to make sure I wasn't missing something obvious.

 

[soccerdad]

If the valve is leaking, then you can see it leaking inside the ski when underway with the seat off. Maybe that is what they were saying.

 

[racerxxx]

Is there a water stain under the wcv running down the water box? That's a dead ringer right there.