What happens when the primary circuit in a magneto ignition system opens?

In a magneto ignition system, the primary circuit is essential for creating a magnetic field that leads to the generation of a high-voltage spark. When the primary circuit opens, the sudden collapse of the magnetic field induces a high voltage in the secondary coil of the ignition system. This high voltage is what generates a spark at the spark plug, igniting the air-fuel mixture in the engine cylinder.

This phenomenon relies on electromagnetic induction, where the change in magnetic flux due to the opening of the primary circuit leads to this induction process. Therefore, the result of opening the primary circuit is indeed the generation of a spark, which is crucial for the engine's operation.

The other options do not directly relate to the primary circuit opening in a magneto system. For example, fuel leaking into the cylinder is unrelated to the ignition process. Similarly, while an engine can stall if the ignition is not functioning properly, that won't occur purely from the primary circuit opening; it needs context regarding the engine's operation. Finally, the battery discharging is not applicable here because a magneto ignition system typically operates independently of a battery once the engine is running. Thus, the generation of a spark at the spark plug is the direct effect of the primary circuit opening.