The fuel mixture is too rich and the engine oil is leaking.
1. The combustible mixture is too rich: the remaining unburned portion will accumulate on the spark plug electrode and become charred. The fuel mixture is too rich, which will cause the spark plug to flash abnormally until it is damaged. carbonization.
2. Oil leak in the engine: During engine operation, if blue or black smoke is emitted from the exhaust pipe, it indicates that oil is leaking from the engine, causing the production of a spark from the spark plug electrode. a large amount of carbon deposits, otherwise it may be wet by oil and unable to jump.