Top spark plug Top spark plug Bottom spark plug Bottom spark plug Cylinder No. 1 Cylinder No. 2 Coil Pack 1 Coil Pack 2 GLYPH<0>CGLYPH<0>H GLYPH<0>A GLYPH<0>NGLYPH<0>N GLYPH<0>E GLYPH<0>L GLYPH<0>1 GLYPH<0>CGLYPH<0>H GLYPH<0>A GLYPH<0>NGLYPH<0>N GLYPH<0>E GLYPH<0>L GLYPH<0>2 Electronic Control Unit 1 Figure 4-23.  Ignition control. engine starting systems normally include one of the following  types of auxiliary starting systems: booster coil (older style),  starting vibrator (sometimes called shower of sparks),  impulse coupling, or electronic ignition systems. NOTE: Engine ignition timing is established by the ECUs  and cannot be manually adjusted. During engine starting, the output of a magneto is low  because the cranking speed of the engine is low. This is  understandable when the factors that determine the amount  of voltage induced in a circuit are considered. During the starting cycle, the engine is turning very slowly  compared to normal speed. The ignition must be retarded  or moved back to prevent kickback of the piston trying to  rotate opposite normal rotation. Each starting system has a  method of retarding the spark during starting of the engine.  To increase the value of an induced voltage, the strength  of the magnetic field must be increased by using a stronger  magnet, by increasing the number of turns in the coil, or by  increasing the rate of relative motion between the magnet  and the conductor. Since the strength of the rotating magnet and the number  of turns in the coil are constant factors in magneto ignition  systems, the voltage produced depends upon the speed at  which the rotating magnet is turned. When the engine is  being cranked for starting, the magnet is rotated at about  80 rpm. Since the value of the induced voltage is so low, a  spark may not jump the spark plug gap. To facilitate engine  starting, an auxiliary device is connected to the magneto to  provide a high ignition voltage. Used mainly with older radial engine ignition systems,  the booster coil assembly consists of two coils wound on  a soft iron core, a set of contact points, and a condenser.  [Figure 4-24]  The booster coil is separate from the magneto  and can generate a series of sparks on its own. During the  start cycle, these sparks are routed to the trailing finger on  the distributor rotor and then to the appropriate cylinder  ignition lead. The primary winding has one end grounded at  the internal grounding strip and its other end connected to the  moving contact point. The stationary contact is fitted with a  terminal to which battery voltage is applied when the magneto  switch is placed in the start position, or automatically applied  when the starter is engaged. The secondary winding, which  contains several times as many turns as the primary coil,  has one end grounded at the internal grounding strip and the  Ordinarily, such auxiliary ignition units are energized by  the battery and connected to the left magneto. Reciprocating  4-15 Booster Coil Auxiliary Ignition Units