The relative proportions of air and fuel entering an engine's cylinders as produced by the carburetor or fuel-injection system; the measure of the amount of air and fuel needed for proper combustion. The ideal or stoichiometric ratio for gasoline is 14.7: 1 air to fuel by weight. A higher ratio would contain more air and less fuel, and would be considered a lean mixture. A lower ratio with more fuel and less air would be a rich mixture. The air/fuel ratio is determined by the orifice size of the main jets inside a carburetor, the dwell duration of the mixture control solenoid inside a feedback carburetor, or the orifice opening and fuel pulse duration of a fuel injector.