What should I pay attention to when replacing spark plugs?

When replacing a new spark plug, care should be taken to compare the lengths of the external threads of the new and old spark plugs. If the thread of the new spark plug is too short, the spark plug gap will be located in the depression of the cylinder head, and the arc will be difficult or even impossible to ignite the mixture.
If it is too long, the exposed bottom of the spark plug will overheat, causing premature combustion, and the threads protruding into the combustion chamber will deposit carbon, and the end of the spark plug may even hit the top of the piston.
Before removing the spark plug, remove debris and dust from the spark plug hole. If there is dust and debris in the spark plug hole, you can use your mouth to blow off the dust and debris; if it is not easy to blow off, you can use a rag and a screwdriver to remove it.
When removing the high-voltage branch line, the marks of each cylinder should be done well to avoid disordered ignition sequence when reinstalling. When disassembling the high-voltage branch line, do not grab the wire and yank it, but grab the dust cover at the end of the high-voltage branch line. The spark plug can be removed after the engine is cooled down. When the spark plug to be removed is unscrewed, use a thin hose to blow off the dirt around the spark plug to prevent the dirt from falling into the combustion chamber after the spark plug is unscrewed.