The quickest way to make your 125cc Roadwin run faster is remove entire factory plastic air breather assembly and install simple K&N foam air fliter..cost about 20 bucks..Next remove chrome muffler part of exhaust pipe..drill out the rivets holding the baffle..remove baffle and take a 15inch long or longer punch and knock bigger holes in the deflector plate in the muffler..discard baffle and rivet chrome end cap back on the muffler...next remove rear wheel and change rear sprocket to one that is 2 teeth less than the factory sprocket.I did this to my roadwin and it picked up 8 miles per hour faster than stock..top speed before with 180 pound rider 63mph after 71mph..I had it almost up to 80mph on a slight downhill..SCARY...!!