50mm bore single piece cylinder/head (increased weight capacity, lower operating temps, easier starting, sustained power output across varied rpm range) Upgraded Tunable High Performance Carburetor. Features: Choke lever on the handlebars, Main jet. (Can be re-jetted), Pilot jet, Copper oil needle, Idle RPM Screw, Idle Air Screw that delivers more fuel with the choke on, instead of restricting air. Great for cold weather starts! 4 bolts attach the engine to your bike frame and this kit comes are 8mm vs the standard 6mm. That means the mounts are twice as strong and twice as secure.