Zippers Performance Z113-016 Thunderjet Black for S&S E/B Carbs/Keihin & Bendix CarbsThunderJet is a jet able, externally mounted third fuel circuit that improves the performance of 2 circuit carbs such as the S&S Super. Unmodified, these carbs typically have a low speed, or intermediate, circuit that supplies fuel from idle to approximately 2500 rpm, at which point the carbs main jet circuit becomes active, delivering more fuel to the engine. These two circuits must then supply fuel for the rest of the rpm range. The problem is: the