Method and apparatus for controlling the ignition timing of an internal combustion engine

Apparatus for controlling an ignition timing of an internal combustion engine provided with an exhaust gas purifying catalytic converter, comprising:

• means for detecting a selected property of a fuel supplied to the engine and for generating a corresponding first signal;
• means for determining a retard angle setting amount for the engine in correspondence with the first signal;
• means for controlling an ignition device to set an ignition timing retard angle of the engine, during a predetermined interval after engine start-up, using a retard angle correction amount selected in correspondence with the determined retard angle setting correction amount;
• means for adjusting the retard angle correction amount to a progressively smaller value the heavier the detected property of the fuel and to a progressively larger value the lighter the detected property of the fuel;
• and
• means for setting the retard angle correction amount to a level at which there is an increase in hydrocarbon amount in the exhaust gas to obtain an increase in catalytic converter activity.