Zippers ThunderJet Kit for S&S E and B Carbs - Blue 113-015 ThunderJets patented third fuel circuit delivers needed fuel to the engine only at higher rpm (4,500 and up) Allows use of the main jet to tune for smooth, broad mid-range powersupplement the top-end with the ThunderJet Jets are used to control the amount of fuel sent to the engine Comes with complete installation/tuning instructions and extra jets The system can operate over a wide range of altitude and atmospheric conditions