Leakage of the cylinder will cause the combustible mixture to have insufficient pressure, which will inevitably cause the engine to fail to start. The method of inspection is to turn the crankshaft by hand. If there is no resistance or the resistance is very small, it indicates that the cylinder is leaking and should be repaired in time. Excessive carbon deposit in the exhaust pipe or blockage due to dirt will cause excessive exhaust gas in the cylinder, which will inevitably affect the ignition of the combustible mixture and cause the engine to fail to start. The method of elimination is to remove the exhaust pipe and remove the carbon deposits and dirt in the exhaust pipe (including the muffler).