Briggs & Stratton World Formula Adjustable Jet Kit - 557012 - WKA / IKF LegalDialing in the exact stoichiometric ratio dictates your corner exit speed, which is why every top tier go kart shop relies on the Briggs & Stratton 557012 Jet Kit for immediate trackside calibration. When density altitude shifts between morning practice and the afternoon main event, swapping your main and idle jets is the only way to keep your engine operating at peak volumetric efficiency. This kit empowers methodical racers to lean out the mixture