How does mechanical ignition spark advance modify timing?

Mechanical ignition spark advance modifies timing primarily by physically moving the pulsar coil. The pulsar coil plays a critical role in generating the ignition signal at the correct moment during the engine's cycle. By adjusting the position of the pulsar coil, the ignition timing can be advanced or retarded, effectively changing when the spark plug fires relative to the position of the piston in the cylinder.

The timing of the spark is crucial for optimum engine performance and efficiency because it determines the exact moment the air-fuel mixture ignites in relation to the piston’s position. Advancing the timing can lead to better performance by allowing for more complete combustion of the fuel, while retarding it can help to prevent knocking and engine damage.

The other options do play a role in engine operation and performance but do not directly relate to the mechanical modification of ignition timing in the way that adjusting the position of the pulsar coil does.