Ignition Timing

Ignition timing is the moment the spark plug fires relative to the crankshaft position. It is expressed in degrees before top dead centre (BTDC). Because the mixture takes time to burn, the spark must fire slightly before the piston reaches the top, so peak pressure arrives just after it.

As engine speed rises, the spark needs to fire earlier, which is called advance. Modern electronic ignitions and ECUs adjust timing continuously according to rpm, load and sometimes knock sensors.

Timing that is too advanced causes detonation (pinking), which can damage pistons; too retarded timing loses power and makes the engine run hot. On most modern bikes timing is not adjustable, but on older and some two-stroke engines it is set by rotating the stator or pickup.