1. The air filter is not working properly. When maintaining the air filter, if too much oil is added to the oil bath air filter, it will cause the engine oil to enter the cylinder under strong suction during operation, causing a feeling of excessive fuel concentration. Due to the high viscosity of the oil, some of it adheres to the intake pipe wall, and the oil entering the cylinder cannot be completely burned. During the exhaust process, the oil is discharged and partially adheres to the exhaust pipe wall. Under the high temperature of the exhaust gas, it continues to burn, causing the temperature to gradually increase, causing the exhaust pipe to burn red and emitting a detonation sound. After disassembling the intake and exhaust pipes, scraping off any oil or carbon deposits, the fault can be eliminated.

2. When the valve timing is incorrect or the gap between parts is not correct, the symptom of exhaust pipe fire is that the fire is burning rapidly, but there is no smoke. The reason is often due to possible deviations in the keyway on the camshaft, deviation in the included angle of the camshaft, or disordered gear markings. Incorrect valve timing refers to the reaction between the early opening and closing of the intake and exhaust valves when the piston reaches top dead center, and the angle of rotation of the crankshaft does not meet the specified value. At this point, the combustible mixture in the cylinder burns inside and outside the exhaust valve due to the early opening of the exhaust valve, causing the engine exhaust pipe to flash. At the same time, the exhaust temperature is high because Heat of combustion cannot be dissipated

3. If the fuel supply time is too late at this time, it will cause the fuel to not burn completely in the cylinder, and after entering the exhaust pipe, it will encounter overheated air, causing the exhaust pipe to emit red flames. The characteristic of this fire is its moderate intensity.

4. Improper operation of the governor When the speed control lever of the engine governor is in contact with the speed control slider, the cone angle of the slider during movement is not appropriate, which can cause the fuel supply of the fuel injection pump to fluctuate, causing the exhaust pipe to spray fire. At this point, the characteristic of the fault is a large and flickering fire.