Welcome to the forum. Look around and read some here. You'll find a lot of good information. Wildalaskan is right on regarding the expansion exhaust for a two stroke (if that's what you're running) as it instantly makes a big improvement. The Sick Bike Parts exhaust is a well made, well thought out setup worth checking... one of our vendors here.
Someday when I grow up I will probably lose interest in toys with wheels, but until then...