Edelbrock Thunder Series AVS Carburetors 1812 These carburetors have all of the performance features of Edelbrock's Performer carburetors, with an added twist--the Qwick Tune secondary air valve. This air valve can be easily adjusted to kick in the secondaries early or late--no extra springs are needed. These CNC-profiled, ball-burnished aluminum carbs feature black accented hardware and GM/AMC throttle linkage. Also included with every Edelbrock carburetor is an owner's manual. These manuals consist of two sections: Section 1, Theory of Operation and Tuning Procedures, will help you to develop your own individualized calibration. Section 2, Tuning Procedures, will take you through a step-by-step procedure that will enable you to achieve a desirable calibration. For added ease of tuning, a calibration reference chart for your model of carburetor will be included.