No, they burn about as cleanly as any U.S. engine designed in the 1960’s. The Russians pack a lot of thrust in their engines, but reliability and availability of spares and manufacturer level maintenance have been an issue for foreign buyers.
The best axioms regarding anything Mil from Mother Russia:
First and foremost they are mostly effective against poorly armed and civilians.
Second, their stuff (other than the AK) carry a dismal track record against US or European mil equip.
Third, as you pointed out are a maintenance nightmare for field users.
Fourth, even though they have top notch industrial spys, the stolen tech design info rarely reaches the drawing desk or factory floor effectively.
Fifth and most importantly, Russian Mil is as stupidly braggadocios as are the Arabs while putting minimal emphasis on design and build quality. Could be its mostly meant for Russian national consumption.