Also,one thing some guys get confused on is the throttle controls the amount of air entering an engine.The displacement of any given engine never changes,so the volume of air pulled into the engine is constant for any given rpm.The throttle blade blocks different ports at different positions,and therefore changes the DENSITY,or richness,of the A/F mixture.Throttle plates control the engine speed by changing the density of the A/F mixture,not the amount of air supplied to the engine.