Dual schedule ignition system

An ignition system for an internal combustion engine, such as an outboard marine engine, which includes an advanced timing schedule, a normal timing schedule, and a circuit for switching between the two schedules or disabling both schedules based upon engine operating conditions. The ignition system includes an optoelectronic time base generator which produces two sets of timing pulses relative to crankshaft position which are normal timing pulses and advanced timing pulses. The time base generator comprises a LED-phototransistor pair and an encoder disk attached to the crankshaft with slots to interrupt the emission path between LED-phototransistor pair. The normal pulses are generated based upon the trailing edge of each slot while the advanced pulses are generated based up the leading edge, wherein the width of the slots indicate the degree of advancement of the advanced schedule over the normal schedule. Both schedules are inhibited based on a high overspeed condition and a low overspeed condition when the engine is overheated, wherein there is a smooth tarnsition between the two conditions.