how to fix carbon problem in yukon 1997 " bad smell and balck air "

Black, sooty exhaust could be due to excess fuel pressure/running rich. That can have a few reasons; O2 sensor(s), ECM fuel and/or ignition mapping including MAP/MAF sensor, throttle/spider gears, fuel injectors (would have to check with noid light, pulse may be on too long). You also mention a "bad smell" if that smell is like rotten eggs it's a good indicator catalytic converter is plugged, which would also affect downstream O2 sensor. You don't mention it running rough or poor performance, so I'd focus on cat.