Which two circuits comprise ignition systems in four-stroke engines?

The correct choice reflects the fact that ignition systems in four-stroke engines consist of two key circuits: the primary circuit and the secondary circuit.

The primary circuit is responsible for carrying low voltage from the battery or ignition coil to the ignition module or points. It controls the initial charge and timing of the ignition system. When the ignition key is turned on, this circuit builds up an electromagnetic field in the coil.

The secondary circuit then takes the energy from the primary circuit and transforms it into a high voltage necessary to ignite the air-fuel mixture in the engine's combustion chamber. This is done through the ignition coil, which steps up the voltage to the range needed for spark generation, allowing for efficient combustion.

Understanding these two circuits and their interaction is crucial for diagnosing and troubleshooting ignition system issues in four-stroke engines, making it an essential aspect of small engine technology.