content_image/608251.jpg
times as many turns in the secondary as in the primary, the induced voltage that results from lines of force linking the secondary is high enough to furnish ignition for the engine. 

The condenser, which is connected across the contact points, has an important function in this circuit. [Figure 4-25]  As current flow in the primary coil is interrupted by the opening of the contact points, the high self-induced voltage that accompanies each collapse of the primary magnetic field surges into the condenser. Without a condenser, an arc would jump across the points with each collapse of the magnetic field. This would burn and pit the contact points and greatly reduce the voltage output of the booster coil. The booster coil generates a pulsating DC in the primary winding that induces a high-voltage spark in the secondary windings of the booster coil. 

## Impulse Coupling 

Many opposed reciprocating engines are equipped with an impulse coupling as the auxiliary starting system. An impulse coupling gives one of the magnetos attached to the engine, generally the left, a brief acceleration, that produces an intense spark for starting. This device consists of a cam and counterweight assembly, spring, and a body assembly. [Figure 4-26]  The assembled impulse coupling is shown installed on a typical magneto in Figure 4-27 . 

The magneto is flexibly connected through the impulse coupling by means of the spring so that at low speed the magneto is temporarily held. [Figure 4-28]  The counterweight, because of slow rotation, catches on a stud or stop pins, and the magneto spring is wound as the engine continues to turn. The engine continues to rotate until the piston of the cylinder to be fired reaches approximately a top dead center position. At this point, the magneto counterweight contacts the body of the impulse coupling and is released. The spring kicks back to its original position, resulting in a quick twist of the rotating magnet of the magneto. [Figure 4-29]  This, being equivalent to high-speed magneto rotation, produces a spark that jumps the gap at the spark plug electrodes. The impulse coupling has performed two functions: rotating the magneto fast enough to produce a good spark and retarding the timing of the spark during the start cycle. After the engine is started and the magneto reaches a speed at which it furnishes sufficient current, the counterweights in the impulse coupling fly outward due to centrifugal force or rapid rotation. This action prevents the two counterweight coupling members from contact with the stop pin. That makes it a solid unit, returning the magneto to a normal timing position relative to the engine. The presence of an impulse coupling is identified by a sharp clicking noise as the crankshaft is turned at starter cranking speed past top center on each cylinder. 

<img src='content_image/608251.jpg'>

problem that can arise from impulse couplings is that the counterweights can become magnetized and not engage the stop pins. Congealed oil or sludge on the counterweights during cold weather may produce the same results. This prevents the counterweight weights from engaging the stop pins, which results i no starting spark being produced. Wear can cause problems with impulse couplings. They should be inspected and any maintenance should be performed as 

