IGNITION LAG CAUSE

The very short period of time which elapses between the instant of action of the mechanism which causes the spark to be produced, to the instant at which the spark actually takes place, e. g., the time elapsing between the closing of the circuit by the timer (q. v.). of a vibrator coil system to the instant at which the spark passes at the plug. 

The time is taken up partly by the electromagnetic actions and partly by the mechanical action of the vibrator. This lag plus the combustion lag represents the total delay between the spark producing action and the attainment of the full working pressure upon the piston and renders variable spark timing desirable in the operation of most motors, especially when battery systems of ignition are used.