Which of the following factors is essential for preventing backfiring?

Effective maintenance of fuel-air mixtures is crucial for preventing backfiring in an engine. Backfiring occurs when the air-fuel mixture ignites in the intake or exhaust system instead of the combustion chamber. This can happen due to an overly rich or lean mixture, which can cause the combustion process to be less efficient and create conditions favorable for backfire.

Properly maintaining the fuel-air mixtures ensures that the engine runs smoothly, with the correct proportion of fuel and air entering the cylinders at the right time. This synchronous action allows for optimal combustion and minimizes the chances of unburnt fuel being ignited in the exhaust system, which leads to backfiring.

In contrast, while the other factors such as engine size, lubrication, and exhaust systems contribute to overall engine performance and reliability, they do not specifically address the intricate balance of fuel and air that is paramount in preventing backfiring.