It is because of the design of the RD-33 engine combustion chamber on the earlier engines. The Klimow RD-33 was the first Russian turbofan jet engine in mass production. It has a one stage injector which is not as efficient as many western designs. A new version of that engine (RD-33MK) doesn’t smoke as much. Poland’s MiG-29s do not have upgraded engines because of political reasons and cost.
Sometime around 1998, Petr Izotov, V.Ya.Klimov plant chief designer was quoted as saying: “Smoke is absolutely subjective. It would be a problem if it would affect plane’s flight performance or engine characteristics. But it doesn’t!” Obviously the operational implications of being seen at much longer ranges was not mentioned.
