A-B1694926-AI VALVE-IDLE MIXTUREOne New Aftermarket Replacement Idle Mixture Valve Fits Briggs and Stratton (Fits Briggs & Fits Stratton) Small Engines This aftermarket replacement idle mixture valve (also called a needle valve or idle mixture screw valve) is a carburetor component that regulates the fuel to air mixture at idle on Fits Briggs and Stratton small gasoline engines. A worn or damaged idle mixture valve causes rough idling, poor throttle response, and hard starting on