What is the optimum air/fuel ratio for normal combustion in a four-stroke engine?

The optimum air/fuel ratio for normal combustion in a four-stroke engine is 14.7 parts of air to one part of fuel, often referred to as the stoichiometric ratio. This balanced ratio is crucial for achieving complete combustion, which ensures that all the fuel is burned, maximizing power output while minimizing exhaust emissions and unburnt fuel.

At this ideal ratio, the engine can operate efficiently, providing the right amount of oxygen to combust the fuel completely. An imbalance in the air/fuel mixture can lead to combustion problems, such as misfires, poor fuel efficiency, and increased emissions. For example, too much fuel (a richer mixture) can result in incomplete combustion, while too much air (a lean mixture) can lead to overheating and potential engine damage. Therefore, maintaining this optimum ratio is vital for the proper operation of four-stroke engines.