The Edelbrock Thunder Series Electric Choke New Carburetor features unique AVS (Adjustable Valve Secondary), which allows simple and accurate tuning of the secondary circuit with simple hand tools while installed on the vehicle. The counterweighted secondary design utilizes a heavy, non adjustable counterweight that relies on the velocity of the air coming through the secondary venturis to roll open the secondary air door, thus helping to eliminate primary to secondary stumbles. The newly designed primary and secondary booster clusters offer the most accurate and up to date calibration available. The outside of the carburetor body is ball burnished for a bright finish. There are no gaskets below the fuel bowl level for a leak-free operation. The carburetor two-piece design makes it easy to change jets or adjust the floats. The needles, springs, jets and floats can be replaced and tuned without draining the fuel. Complete tuning can be done without removing the carburetor from the intake manifold.