basically mixes fuel and air and directs the mixture into the engine. on average 15 parts air to 1 part fuel. go to the local library can find a lot of books on motorcycle mechanics. they have all u want to know.Originally posted by tOngEh:a device that control ur air, oil flow depending on the external devices like: exhuast,reed valves,CDI, or anything that associate with oil and air intake that slower or increase ur movement.