Ignition Timing: Specifications
The 
ignition timing is normally 
10 ° BTDC but is retarded when the temperature of the intake air exceeds 
4 ° C.  When the temperature of the intake air reaches 
100 ° C, the ignition advance is 
3 ° BTDC.  The reason for retarding the ignition when the air temperature rises is that the combustion speed then increases as well.