1, take out the spark plug
2, use metal wire or needle to remove the carbon deposition on the spark plug, adjust the valve clearance to 0.6-0.8mm.
When removing the carbon deposition, please observe with attention the color of the appearance of spark plug and carbide. We can judge if the spark plug fits or not by observing the color. If the standard spark plug is easy to damp, you should replace by heat type spark plug; if the standard spark plus is easy to be heated (porcelain pole change white), then you should replace by cold type spark plug.