The water box valve did have a little water and gunk inside the bellows. I didn't notice a tear in the bellows, but I may just swap it out with the donor bike. Is the water box valve related to the RAVE valve solenoid?
The water box valve is a completely separate system from the RAVE valves, despite they are both installed in and control aspects of the exhaust system (emphasis on system), the water box valve simply controls the volume of water injected to the expansion pipe (sometimes called the cone pipe) to adjust the sonic length of the expansion pipe for a sort of "turbocharging" effect.
Concerning the RAVES, it's purely a coincidence the valves look similar, they're made by the same vendor I guess and probably they designed the entire tuned exhaust system.
In the case of the RAVES, these control the size(cross section) and timing of the exhaust ports in the cylinders. During low speed operation, it helps to have a conservative(retarded port timing) exhaust port configuration in order to obtain acceptably smooth operation and throttle response. During low speed operation, the RAVE valves are closed in order to reduce the exhaust port cross sectional area and retard the porting of the exhaust stroke. This helps to take some of the edginess out of the tune in order to improve low speed performance. If the RAVES were always up in their opened position (advanced port timing), the engine wouldn't idle well, and would be difficult to start.
But open up the throttle a good ways approaching greater than 50%, and restricted exhaust ports(RAVES closed) will restrict the way the engine breaths, so the RAVE valves should begin opening to allow the engine to breath and make use of the tuned exhaust expansion pipe.
So if your RAVES aren't fully opening (lifting completely up, advancing the exhaust port timing) for whatever reason, then the engine cannot develop it's full potential power b/c the exhaust port timing is too retarded. Conversely, if the RAVES are sticking open then low speed operation will be mushy and difficult to control, resulting in poor throttle response, and possibly hard to start the engine.
Story short, the MPEM energizes the solenoid based on MPEM pre-mapped programming (basically engine RPM, I think), which allows air pressure from the crankcase through the solenoid to pressurize the RAVE bellows and actuate the blade upward, advancing the exhaust port timing.
So if there's something wrong with the air solenoid for whatever reason (perhaps the electrical connector is disconnected), then the RAVE valves won't receive air pressure from the crankcase and they won't open. This will limit engine performance. If I recall, my 951 engine wouldn't rev to 6000RPM when I first splashed my newly bought used boat until after I removed the RAVES and cleaned the carbon and oil film that was causing them to stick in the closed position. I seem to recall it would only rev to about 5600 RPM.
Otherwise, there may be some other phenomenon causing your particular performance issue, confirming/maintaining RAVES operation is typically the low-hanging fruit.
Thus, if you're confident the RAVE's system is functioning properly, we can brainstorm further on other possibilities.
