There is obvious arc burn marks along the axial of insulator.
Cause:The service time of spark plugs is too long,melted electrode,gap is too wide,the boot of spark plug wire has poor insulation and is aging. the gap between spark plup wire boot and insulator is too wide.
Action:change spark plug wire or smear silicom oil in spark plug wire.Adjust the spark plug gap or change spark plugs.
