1, the piston ring is not tightly engaged with the cylinder wall, the gap between the piston ring openings is too large or all the ring openings overlap in the same direction, the cylinder wall scratches the groove, the piston ring elasticity is too weak, and the piston ring bites into the ring groove. After the engine speed is stable, connect the spark plugs of each cylinder with awl in turn.
2. When the air leakage is serious, pull out the piston for inspection. When the piston ring is engaged, the carbon deposit should be removed, and the port should be matched and adjusted according to the regulations; The elasticity of piston ring is too weak, and the wear of cylinder liner is too serious. The piston ring should be replaced and the engine repaired.