Ignition timing Ignition timing In a spark ignition internal combustion engine, Ignition timing refers to the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need for advancing (or retarding) the timing of the spark is because fuel does not completely burn the instant the spark fires, the combustion gases take a period of time to expand and the angular or rotational speed of the engine can lengthen or shorten the time frame in which the burning and expansion should occur. In a
Dual ignition single point of failure in mechanical terms, that could cause both ignition systems to cease working. A simple form of partial dual ignition on some amateur-built aircraft uses a single spark plug, but duplicates the coil and pick-up for better redundancy than traditional single ignition. A further form of partial dual ignition (such as on the Honda VT500) is for each cylinder to have a single HT coil which sends the current to one plug and completes the circuit via the second plug, rather than via the earth. This system requires a voltage sufficient to jump both plug gaps, but