The RAVE, (Rotax Adjustable Variable Exhaust) valves are located above the exhaust valve. There are 2 of them per engine. They are round with a red adjustment screw in the middle. It has a clip that holds it together. How they work is that they open the exhaust port larger as the engine rpm's increase. When the rpm's drop down so do the RAVE valves. They work on the principle of the pressure of the exhaust system. Rpm's increase, pressure increases and the valve opens, rpm's drop pressure drops, Valve closes. They should be de-carbonized annual. To disassemble the rave valves, remove the spring clip on top, remove the black cover. There is a spring under the cover. Remove the piston by turning it with a metric socket. On the bottom of the piston is the rubber "Bellows" be careful with the small retaining spring that hold the bellows on the piston. Remove the 2 allen screws that hold the base on the cylinder. Remove the base and gasket. The long valve won't fall in the cylinder just pull it out. There is an o ring under the base, on the shaft of the guillotine valve. Be careful to see how it came apart as it has to go back together that same way again. On the base, notice the notch that it is facing down. Clean all the carbon off the guillotine valve. I use carb cleaner and 400 grit paper. A large wire wheel also works real well. Check the bellows for any small pin holes. If so replace it. If not, reassemble it on the clean guillotine valve, and install it back on the engine the same way it came apart. The guillotine valve only fits one way. The one closest to the exhaust pipe will come off differently then the other one. You will have to remove the allen screws and turn the base so it clears the exhaust pipe. I would do one at a time in case you forget how it goes back together again. This way you can look at the other one and copy it. Do both engines 2 per engine. Take your time and if you have questions give us a shout. We'll be here to help you out.
A loose fit is nessesary and normal though. The valves get very hot and expand, so loose clearances are necessary. But if the shafts have any wear on them, or the holes in the housings are getting oval shaped, you need to replace them. An up-grade "slotted rave" is now available and works excellent!
The water regulator (WR), It will change the timing of when water gets injected into the pipe, which changes the performance a bit. It will not make your boat faster, but is an aid to the accelleration curve. Typically, the WR red cap is the opposite of where the RAVE caps are set. So, if the raves are adjusted outward, the WR cap in adjusted inward or vise versa. Adjusting the WR spring tension valve will either just delay or speed up when the valve opens.
If the RAVE valves are dirty it will not rev up correctly and could be causing your problem. On 787 engines the red adjuster knob should be flush with the top of the cover, for 951 engines it should be fully tightened in the cover bore. at that setting the pipe is dried out somewhat allowing the engine to rev higher.Changing the adjustment will only change the amount of water that is injected into the headpipe. Having said that, if you were to actually completely pinch off the water line from the regulator to the headpipe, the exhaust chamber would overheat and melt the hoses. That's about as catastrophic as it would get. The engine itself (or the cooling to the engine) would not be affected at all.
pressure line runs from....... pulse fitting under carbs to check valve to rave solenoid, rave solenoid actuates raves around 4500ish rpm by opening pressure to diaphragm. closes by solenoid opening to atmosphere on most all 951's. remove, it should move freely in housing. if not inspect and clean. the shop manual has some spew about no parts wearing, but diaphragm can tear, piston shaft can wear and not seal on oring causing leak/black oily goo..... it takes very little pressure to actuate valves, pull line and pressurize with pop off or blow hard. Clean any accumulation of sand out of the small hose going to pipe belly & make sure there is no blockage in the fitting with A wire or pointed tool. You can feel a surge at
about 4400 rpm operating range when the raves open.
