Ignition timing dictates precisely when the spark plug fires to ignite the air-fuel mixture in a cylinder. It is measured in degrees of crankshaft rotation before top dead center (BTDC). Proper timing ensures peak combustion pressure hits just as the piston begins its downward power stroke, maximizing engine efficiency and preventing damaging detonation.
Hook up the timing light and see if the ignition timing is set to 10 degrees before top dead center like the manual says.
Advancing the timing fires the spark earlier to make more power at high RPMs, but going too far causes engine knock.
Related terms
Top dead center
The exact point in engine rotation where a piston reaches its highest position in the cylinder.
Detonation
An uncontrolled secondary explosion in the combustion chamber that causes severe engine damage.
Basic ignition timing
The baseline degree of crankshaft rotation at which the spark plug fires during idle.