Final answer:
A common ignition system problem experienced with rotary lawnmower engines is engine knocking or pinging due to low octane gasoline. This can result in rough running, loss of power, and potential engine damage.
Step-by-step explanation:
A fairly common ignition system problem experienced with engines powering rotary lawnmowers is engine knocking or pinging. This occurs when the gasoline used has a low octane rating, causing premature ignition and uneven burning of the fuel. Engine knocking can lead to rough running, loss of power, and potential damage to the engine.
To fix this issue, it is important to use gasoline with the correct octane rating recommended by the lawnmower's manufacturer. Additionally, checking and maintaining the spark plug is crucial for proper ignition and combustion.