1980 Pickup 20R Emissions / Running Rich

[GregoryB]

I have a 1980 pickup with 20R stock engine. I'm having problems getting it to pass CA smog test. I've replaced the vacuum lines, had the carburetor rebuilt, mixture screw is about a turn out. Engine runs smooth at 900rpm, can take it lower as well and still have it run smooth. Timing is at 7 BTDC. Vacuum is at 17-18 psi and moves around a little.

Had the carburetor rebuilt before the most recent test and it didn't help at all. CO measures 4.52 and max allowable is 1.62. It passes on the NO and HC test, only fails CO. Mechanics told me it's running too rich and its pretty fumy when running. I've seen posts about the AAP and pulled that hose when the engine is warm, didn't see any gas. What other things should I be looking into?

 

[liveoak]

Does the 1980 truck have an egr valve? After rebuilding my 22re my vacuum increased causing the EGR to open too soon resulting in random misfire causing a rich reading. I had to put a washer between the EGR and the intake manifold to reduce the flow. I know yours is carb but you should look into any possible cause of a misfire which could cause a rich reading.

 

[Phares]

You have an EGR valve behind the carb. My line was completely broke in two. I'd start there.