What is the difference of the ignition timing advance and retard?

Answer 1

Ignition timing is setting the point at which the sparkplug fires relative to where the piston is in the cylinder. The highest point the piston can go is called top dead center, or TDC. Timing is set for a number of degrees of crankshaft rotation BEFORE TDC; the number of degrees is determined by the factory, and since it's setting the plug to fire before TDC, it's called the "timing advance". If you set the timing to be closer to TDC than the factory setting, you're reducing the advance, or "retarding" the ignition timing. If you set it to be farther from TDC, you're "advancing" the timing. Changing the timing can dramatically change a motor's power and efficiency. The reason you set the timing before TDC is that you want the exploding gas to be compressed by the upward-moving piston and force the piston back down, generating power. If you retarded the ignition so far that the plug fired after TDC, the piston would already be moving down when the gas exploded and you'd waste most of the energy from the explosion.