Grounding the magneto primary circuit serves to:

• A. Increase spark energy
• B. Provide a return path to stop magneto operation when Off
• C. Improve rotor timing
• D. None of the above

Answer: (B)

Grounding the magneto primary circuit is a way to kill ignition. In a magneto, current flowing through the primary winding while the points are closed builds a magnetic field. When the points open, that field collapses and induces a high voltage in the secondary to fire the spark plugs. If the primary is grounded, there’s no sustained current path, so the magnetic field can’t build effectively and there’s nothing to collapse to generate a spark. With the primary tied to ground when the switch is Off, the magneto is disabled and spark stops. This isn’t about increasing spark energy or changing timing; it’s a deliberate method to shut off ignition across the system.