The ignition maps represent the ignition timing of the spark before top dead centre (BTDC). Please note that the numbers used by different manufacturers do not always represent an exact angle BTDC in degrees (º).
Typically speaking, the values in the ignition map tables are degrees of advance, usually in units of degrees before TDC, but not always (ie. this is manufacturer-specific). Negative values would represent an ignition spark occurring after the piston reaches TDC. In most cases it will not be possible to enter negative values into ignition timing.
Ignition timing is very important because it will affect how efficiently the combustion of the air-fuel mixture translates into power output.
- If ignition timing is set too early, the expansion of gas will try and push the piston downwards while it is trying to move upwards towards the top of its stroke. This can also cause pre-detonation which can increase engine temperatures, and cause severe damage to the engine, particularly under high loads.
- If the ignition timing is set too late, the output will not be used effectively as the expansion of gas will be trying to catch up to the piston while it is already moving downwards. This can also cause backfire to occur from the exhaust.
If you are going to advance the ignition, make sure to make a small change and test the bike before advancing it further. If you increase the ignition advance too quickly, you will risk damaging or even destroying your engine and components.