I have a 1983 Dodge D150 with a slant 6 I took it in for emissions this year and failed on:

HC ppm 4082 Allowed 390 Fail
CO% 6.32 Allowed 3.12 Fail
NO ppm 806 Allowed 2796 Pass
RPM 2400 Max 2500 max
CO+C02% 12.4 6.0 Min.

I adjusted the timing 1/4 turn ahead and had it retested now:
HC ppm 259 Allowed 390 Pass
CO% 7.52 Allowed 3.12 Fail
NO ppm 601 Allowed 2796 Pass
RPM 1664 Max 2500 max
CO+C02% 14.3 6.0 Min.

What do I need to do to get my CO% to pass? Any suggestions would be greatly appreciated.

 

In Iowa we don't have emissions tests thank God
Mine is emissions control free to include the cat.

 

I'm guessing they did the test by hooking a machine up to the exhaust and running the truck?

You'll probably have to replace your catalytic converter. I'm betting the one on your truck isn't functioning at a high enough efficiency anymore.