jet size alone won't make you faster... Your performance is like a balancing act and changing one thing will throw others off. The jet size just gives you an idea of where everything is at. If you increase the amount of gas going in, you need to make sure the carburetor is still getting enough air to mix with the new increased gas flow. If the fuel to air mixture is too rich you'll bog down, and actually lose speed. The best first step to going faster is a better exhast pipe.