Unless you change something else as well as the jet, exhaust, air cleaner etc., changing the jet will not help. This assumes that the jet is the correct size.
Most standard jets run slightly rich to improve engine cooling and leaning it a bit will give you more power but at the risk of siezing the piston.
If you are not getting "4 cycling" at full speed, your jet is probably ok.
As a quick check, you can turn off the gas while riding and if you speed up significantly just before you start to die from lack of gas, you might try a 1 or 2 size smaller jet but you should allways get a slight increase in power as the gas runs out or you are living too dangerously.