There are several situations.
The spark plug gap is too large. Spark plug breakdown voltage increases due to excessive gap.
Staining or oil leaking on the spark plug ceramic insulator. If the small ceramic head has more carbon deposits or the gasoline contains metal additives such as MMT, causing residue to stick to the small ceramic head, this will also cause flashover and inflammation of the small ceramic head. ceramic head.
The rubber sleeve of the ignition coil (or cylinder wire) is getting old. The rubber sleeve of the ignition coil (or cylinder wire) has cracks and breaks in the inner wall due to high temperature aging.