During a magneto check, which criterion is used for acceptable performance?

During a magneto check, which criterion is used for acceptable performance?

• A. Less than 60 RPM difference
• B. Less than 100 RPM drop L/R
• C. Less than 125 RPM drop L/R, less than 50 RPM difference
• D. Less than 70 RPM difference

Answer: (C)

In a magneto check, you’re looking for both consistent performance and balanced output from the two magnetos. The test checks two things: how much rpm the engine loses when you disable each magneto, and how close the two magnetos are in their output when both are running. Acceptable performance means the rpm drop with either magneto isolated is less than 125 rpm, and the difference between the left and right magnetos when both are enabled is less than 50 rpm. This ensures each magneto is delivering similar spark energy and timing to all cylinders. If the drop exceeds 125 rpm for one side, or the two magnetos differ by more than 50 rpm, it points to a weakness or imbalance in the magneto system, which could cause rough running or misfiring. The other options only reflect part of the requirement or use different thresholds, so they don’t guarantee both adequate drop and good balance.

In a magneto check, you’re looking for both consistent performance and balanced output from the two magnetos. The test checks two things: how much rpm the engine loses when you disable each magneto, and how close the two magnetos are in their output when both are running. Acceptable performance means the rpm drop with either magneto isolated is less than 125 rpm, and the difference between the left and right magnetos when both are enabled is less than 50 rpm. This ensures each magneto is delivering similar spark energy and timing to all cylinders. If the drop exceeds 125 rpm for one side, or the two magnetos differ by more than 50 rpm, it points to a weakness or imbalance in the magneto system, which could cause rough running or misfiring. The other options only reflect part of the requirement or use different thresholds, so they don’t guarantee both adequate drop and good balance.