1971 Johnson 125HP outboards Service Manual, Page 33Get this manual
DESCRIPTION The new capacitor discharge -'C.D ignition system, which is standard equipment of the 125 HP model, consists of three major electronic componentsThese are (1) Coil, (2) Sensor, and (3) Pulse Pack AssemblyThe Sensor, located within the distributor, replaces the breaker points and condenserSee Figure 4-1The Pulse Pack, which is completely sealed in epoxy, is attached to electrical component bracket at the rear of the power head
DO NOT ATTEMPT TO OPEN THE PULSE PACK AS THIS WILL VOID THE WARRANTYTo compliment the C.Dignition system, special surface gap spark plugs are usedThese are Champion L-77V (OMC Part Number 384751)THEORY OF OPERATION The I'ansistorized converter in the pulse pack changes the 12 volt battery supply to 300 volts and stores it in the energy storage capacitorNUT
The triggering circuit, also in the pulse pack, senses the distributor rotor position and closes an electromc switchThis discharges the 300 volt energy from the pulse pack storage capacitor into the coil where it is boosted to the 25000 volts available at the spark plugsWhen the storage capacitor has discharged its energy at the spark plug gap, the electronic switch opens and the converter recharges the storage capacitor