Regarding your question, the black smoke from the exhaust pipe may be due to insufficient combustion caused by too much engine mixture. The air filter is too dirty and the vacuum degree is too high, resulting in the phenomenon of more oil and less gas, and the high-pressure ignition system is weak. All these will cause black smoke caused by insufficient engine combustion. The main reason is that the mixture is too rich, because in the case of more fuel and less oxygen, the incomplete combustion of the mixture in the cylinder will pollute the spark plug, resulting in the blackening of the spark plug and poor ignition; In addition, high-pressure fire is weak, and this phenomenon will also occur. I hope my answer is helpful to you.
See more [Suzuki Alto] information:/Suzuki-Alto/