86 B2000 How to adjust the carburetor???

Can anyone tell me how to adjust the fuel mixture setting on a 1986 B2000? I had what I thought were carburetor adjustment problems and fiddled with the adjusting screw setting and now are not sure exactly where it should be. I believe I am running rich since I pulled a couple of spark plugs and noticed a lot of soot. Also my tailpipe is quite sooty. I have seen several post on other forums that talk about this but I still yet to read what I believe is an authorative voice on this subject. My truck use to get 350 miles per tank and now gets hardly 250. Really need to get this fixed with gas at $2.25 per gallon.

You can try adjusting the mixture screw located in the bottom hole of the carb with the roll pin pushed out while backprobing the O2 sensor with a digital meter set to DC volts. Adjust on a fully warmed up engine.

You are looking for a reading of 0.5 volts on a perfect mixture. Rich is 0.5V up to 0.9V. Lean is 0.1V to 0.5V. Test at idle and WOT.

Hope it helps.