ThunderPRO ThunderJet for S&S G/D Carburetors, Blue Fits all S&S 'G' or 'D' Carburetors Most cost effective horsepower per dollar you can buy! ThunderJet is an additional high speed fuel circuit, delivering needed fuel to the engine at higher rpms, 4500 & up. Use the main jet to tune for smooth, broad mid-range power and supplement the top-end with the ThunderJet Join thousands of satisfied customers worldwide!