What does "tuning" an engine involve?

Tuning an engine primarily involves optimizing its performance by adjusting critical parameters such as the air-fuel mixture and ignition timing. This process is essential because these factors significantly influence how efficiently the engine runs and its overall power output. A well-tuned engine will operate more smoothly, have better throttle response, achieve improved fuel efficiency, and produce lower emissions.

Adjusting the air-fuel mixture ensures that the correct ratio of fuel and air enters the combustion chamber for optimal combustion. Similarly, adjusting the ignition timing affects when the spark plug ignites the air-fuel mixture, which is crucial for maximizing power and efficiency.

The other options focus on aspects that might enhance an engine's performance or appearance but do not encompass the tuning process, which is fundamentally about making adjustments for enhanced functionality and efficiency.