Voltage halfwaves generated by a magneto in one polarity are utilized for powering and timing ignition of an internal combustion engine, and voltage halfwaves of the opposite polarity, taken from the circuit of the primary winding, are utilized both to feed a regulated d.c. voltage source for a timing circuit and to provide a recurring trigger voltage for a monostable circuit that keeps the ignition control circuit operative only so long as the speed of the engine does not exceed a predetermined limit. The monostable circuit is constituted by appropriate connecting up of an available timer integrated circuit unit.