Why do we retard?

[sergeantpluck]

This may be a silly question to most, but ....

I know that retarding the ignition to start prevents kick-back, but is this the only reason it's done?
Or does the engine actually run better at slower (kickover speed) revs with retarded ignition?

[Bess]

Hi,
    worth a read:

https://en.wikipedia.org/wiki/Ignition_timing

Best wishes...

[AdrianS]

Primarily to stop kick back when being started.
Most vehicles ( look at a car distributor ) will advance when the engine picks up speed. The momentum of the engine spinning allows the spark to be advanced earlier before TDC. This will ensure a better combustion when the piston is on the down stroke. If the timing was very retarded the piston would be going down the barrel when the mixture ignites due to the time taken for combustion to occur.
This is to maximise the potential power of the engine.

[JOHN KAY]

 HI THERE > I COULD BE WRONG IN SAYING THIS BUT HERE GOES > AS AN ENGINE REVS HIGHER THERE IS LESS AND LESS TIME FOR EXPANSION OF GASES WITHIN THE CYLINDER SO THE SPARK NEEDS TO BE ADVANCED SLIGHTLY TO GIVE IT MORE TIME TO ALLOW IT TO DO THE WORK PROPERLY OR IT COULD UPSET THINGS SOMEWHAT LIKE PRE DETONATION ETC HOWEVER AT TICKOVER AS THERE IS MORE TIME FOR EXPANSION YOU DO NOT NEED TO ADVANCE THE TIMING SO MUCH AND HENCE IT IS RETARDED SLIGHTLY SOMETIMES BY AN AUTOMATIC ADVANCE SYSTEM USING CENTRIFUGAL WEIGHTS AGAINST LITTLE SPRINGS  OR BY MANUALLY DOING IT BY LEVER ON AN OLDER VINTAGE STYLE BIKE  >HOPE THIS HELPS REGARDS JOHNBOY >