gotmy1980

New to the forums here so sorry if i missed this question somewhere else. I am trying to pass smog with my 1980 20r yota. i've gotten it tested twice and the first time i failed HC and CO% on the 15mph test only. I replaced the plugs and wires, cleaned out the carb a bit, new air filter and a new distrubitor cap. It ran a lot smoother than it did before the "tune up" so i figued i would give it a shot..no good. My HC stayed the same as the first test but my CO went from 5.26 to 6.16, while my NOx went down from 157 to 143. Everything else on the truck passed and the 25 mph test passed. I dont want to spend a fortune replacing every part on the carb/engine until it passes any suggestions on what it could be?