What is the maximum RPM drop allowed for a single magnet during a magneto check?

What is the maximum RPM drop allowed for a single magnet during a magneto check?

• A. 100 RPM
• B. 120 RPM
• C. 125 RPM
• D. 130 RPM

Answer: (C)

When you perform a magneto check, you compare the engine’s idle RPM with both magnetos operating to the RPM with one magneto switched off. The idea is to see how much the engine slows down when that magneto is out of the circuit. The limit you’re testing against is 125 RPM for a single magnet. This threshold ensures that even if one ignition source is down, the remaining magneto provides enough spark and timing to keep the engine running smoothly. If the RPM drop exceeds 125, it points to a weak or out-of-spec magneto, coil, or spark plugs and indicates maintenance is needed. The smaller values would be unnecessarily strict, while a value like 130 would exceed the standard limit.

When you perform a magneto check, you compare the engine’s idle RPM with both magnetos operating to the RPM with one magneto switched off. The idea is to see how much the engine slows down when that magneto is out of the circuit. The limit you’re testing against is 125 RPM for a single magnet. This threshold ensures that even if one ignition source is down, the remaining magneto provides enough spark and timing to keep the engine running smoothly. If the RPM drop exceeds 125, it points to a weak or out-of-spec magneto, coil, or spark plugs and indicates maintenance is needed. The smaller values would be unnecessarily strict, while a value like 130 would exceed the standard limit.