JUMP-SPARK IGNITION
In testing an engine fitted with the jump-spark ignition system, the circuit should be closed and the crank shaft revolved twice, attention being paid to the sound of the vibrators. On a four-cylinder engine, the timer makes four contacts in two revolutions of the crank shaft, and if all of the vibrators are heard it is proof that the primary circuit is in good condition, and not the seat of the trouble. If only one of the vibrators buzzes, the battery circuit may be considered to be working properly, for otherwise no current could have passed to the coil box. The trouble may then be identified as being in part if not altogether in the adjustment of the vibrators of the dead coils, their connections with the timer, or in the timer itself. One end of a short piece of wire should be touched to the timer binding post of one of the dead coils, and the other to any metal part of the engine, the lubricator, for instance, to form a short circuit through the primary circuit with the exception of the timer and its connections. If the vibrator buzzes, the trouble is not in the coil, but in that part of the circuit cut out by the short-circuiting wire. The same piece of wire may be used to bridge across to any metal part of the engine from the binding post on the timer at which the wire from the coil is connected, and if the wire from the coil to the timer is in good condition, the vibrator will again buzz, showing that the fault must be in the timer, for all other parts of the primary circuit of that particular coil have been proven to be working correctly. A dirty or faulty contact in the timer, or a loose connection, will probably be the cause.
If the primary circuit is shown to be in good order, attention may at once be given to the gasoline feed, for while the secondary circuits have not been tested, it is extremely unlikely that the spark plugs or their connections will prove defective on all four cylinders at the same time.