The Flow Control Valve Provides improved throttle response and much quicker starts by drying out your waterbox at low rpm and idle speeds. Tests have shown an average acceleration improvement of 10 feet over a non-equipped model in the first 50 feet. The Flow Control Valve allows unrestricted water flow to the Stinger for better top speed. Yet it controls the amount of water at low speeds for better response. It also allows for an easier tuning of the Carburetors. It does not interfere with normal engine or exhaust pipe colling and is compatible with all electronic water injection systems. Race Legal for All Classes. Two Models are available, both are adjustable. The Standard Flow Control Valve is preset at 3.5 psi and is adjusted by adding the supplied stainless steel shims to increase the spring tension. The Pro-Series is externally adjustable by turning the outer housing by hand. Pressure can be tested with pop off gauge. All PWC with OEM & aftermarket exhaust systems EXCEPT Yamaha OEM exhaust.