First of all, consider whether the oil and gasoline meet the standards and whether the oil circuit is smooth, such as whether the oil circuit is blocked because the gasoline filter has not been replaced for a long time, or whether the gasoline pump motor is aging, whether the oil pump is weak, and whether the oil circuit leaks, resulting in fuel leakage.
See if the engine and ignition system are normal. For example, whether the spark plug gap is too large because it has not been replaced for a long time, whether the high-voltage arc is in a bad state, and whether there is leakage in the high-voltage line.
Engine piston ring (gas ring, oil ring) has no blowby. (This is unlikely)
The exhaust system is not blocked. If the exhaust system is blocked, it is very likely, such as three-way catalytic poisoning blockage, or the exhaust tailpipe is thrown into a foreign body and so on. ...