The power valves kit Fit for Holley 4150 4160 M2300 Carburetors #The power valves is a vacuum-operated fuel valve that is designed to enrich the fuel flow to the engine under varied vacuum conditions. It is located in the metering block, and opens at a set vacuum that is determined by the spring it contains. Depending on the spring in the power valve, this can occur at varying engine rpm and directs extra fuel into the carburetor's main power circuit. The valve itself is a small rubber diaphragm with a small coil spring. When opened, it allows fuel to flow through the calibrated opening in the metering block (power valve channel restrictor). This restrictor determines the amount of additional fuel delivered to the engine.