54mm Crankshop. Jetting circuits are based of Mikuni VM jetting. Has a pilot, air jet in the bell, dumptube, main, needle and power jets. The body of the carb is based on crankshop design along with the needle and slide. Thats alot of tuning circuits. Would like to try a 52 Lectron or maybe there new 53mm but those are around 8-900 bucks!!