STOICHIOMETRIC RATIO

For optimum combustion of the air-fuel mixture inside the engine cylinders, there has to be a proper proportion of air and fuel mixed together. Fourteen parts air to one part fuel is the accepted standard, that is, 14:1, also called the stoichiometric ratio. This factors in everything from altitude (at or slightly above mean sea level), air pressure, air density and fuel quality to ensure that exactly enough air is provided to completely burn all of the fuel in the combustion chamber. For example, at higher altitude, a lower fuel-to-air, or leaner, mixture is required to keep the engine running to compensate for poor air density.