A carburetor is actually a tube with an adjustable plate in the middle called a throttle plate that controls the flow of air through the tube. The tube has a constriction called a venturi where a vacuum is created. This constriction has a measuring hole through which fuel can be sucked in by vacuum.
The motorcycle carburetor looks very complicated, but as long as you master some principles, you can adjust the motorcycle to the best condition. All carburetors work on the basic principle of atmospheric pressure. Atmospheric pressure is a powerful force that puts pressure on everything. It will vary slightly, but typically fifteen pounds of pressure per square inch (PSI). This means that atmospheric pressure is fifteen pounds per square inch of anything. By changing the atmospheric pressure inside the engine and the carburetor, it is possible to change the pressure and cause the fuel and air to flow through the carburetor.