These share all the performance advantage of the popular Edelbrock Performer Series with innovative new features. The Qwik-Tune secondary air valve can be easily adjusted to match your needs. Whether you want the secondaries to"kick in"early or late, you can set the air valve using standard tools, with no extra springs. It's a quick and simple process. Qwik-Tune combined with the other great features makes the Edelbrock Thunder Series AVS the most convenient and dependable carburetor available today.