Yamaha F100B F100C Outboards Factory Service Manual, Page 16Get this manual
GEN INFO Ignition system
General information
A CDI system has been incorporatedThe CDI unit uses three signals (i.e crankshaft position, engine revolution, and throttle position) to determine the optimum ignition timingEngine speed is controlled by the CDI unit to prevent damage to the engine when the engine temperature sensor detects that the engine temperature (i.e water temperature) is too high, or when the oil pressure switch detects that the oil pressure is too low, or when the engine idle speed is too highIn addition, when the engine overheats or when there is low oil pressure, the warning lamp flashes and the buzzer soundsIf the throttle position sensor and engine temperature sensor malfunction, the engine ignition timing is set by the CDI unit to prevent damage to the engine