A jet kit is a collection of parts for each carb to alter the air/fuel mixture for improved engine performance. Usually only the main jet is changed along with some internal carb adjustments (idle mixture screws, needle clips, etc.). All of this may sound a little mysterious, but if you look at a parts diagram of a carburetor it will become more clear. Bikes are set up to run lean from the factory to pass emissions regulations. Making the bike draw more air by less restrictive air filter or exhaust causes it to run more lean. Re-jetting richens the air/fuel mixture for better performance.jon341427 said:what is a jet kit? and what is its purpose? whats the difference between a slip on exhaust, and a regular exhaust? and lastly is a seat cowl a replacement for the back seat? or does it just go over the rear seat?