The 'Stoichiometric' air-fuel ratio for gasoline is 14.7:1, and is the ratio at which all of the fuel is consumed. In reality, a tiny amount of gasoline is released in the exhaust as hydrocarbons, 14, I think altogether, and carbon monoxide. Methane is one of the more common hydrocarbons released, and acetlyne is another one, I don't remember the others. Ideally, at the stoichiometric point, there is only water, heat, and carbon dioxide being produced. Richer fuel mixtures than stoichiometric increase fuel consumption and the raise the various components of hydrocarbons in the exhaust stream, but they also give more power. The rich-best-power mixture is about 12.7:1, although that varies slightly with the gasoline blend. A typical cruise mixture for an automotive engine with a properly tuned carburetor was in the range of 13-13.5:1. Some would go leaner than that, but rarely beyond 14.7:1.
In the past, with airplane engines, one method used to reduce fuel consumption for a cruise condition was to lean the fuel mixture beyond 14.7:1 until cylinder head temperature began decreasing, but a flight engineer was watching cylinder head temperature for 72 cylinders- four engines, 18 cylinders each.
But in the real live world of cars and trucks, the best way to determine fuel mixture is to watch the spark plug colors: very clean and white along with slightly bluish electrodes usually indicates too lean; dark brown or dry black indicate too rich. Black and wet indicate oil consumption. Beyond that, both light and dark conditions can be the result of the wrong spark plug (wrong heat range) for the engine.
Harvester
