My 78 was doing the same thing a couple years ago. I never did figure it out though. My dad hollowed out my cat back in the 80s and I think it was the root cause. I four a way to make it pass though. Shoot me a pm if you can't get. it figiured out.

Holley 5200 setup for my 1978 non-Calif model 2.3:
Does this look correct?
PRIMARY JETS:
Plug  170
tube  05
Main  167
SECONDARY JETS:
Plug  185
tube  04
Main  219
Should the primary have a "larger" tube than the secondary? So far, nothing indicates why I am running so horribly rich... all choke components sparkling clean and working properly, same with carb internals. ??

2 things worth checking are: Is the float level and fuel pressure correct? If either of these are too high that will
cause rich condition even at idle because if the fuel level in the idle and main circuits is above the design level
you couldn't add enough air though the main and idle air correction jets to compensate. The other is see if you can find the as delivered air, main jet and emulsion tube configuration for the particular carb by tag number if you can to see if it is currently got
the right parts in the right places.

Let us know if that helps.

Phil

 I will be happy too if it helps let us know. I read you said you completely rebuilt the carb,but you just never know. When you do replace the power valve diaphragm, you can press it down and hold your thumb over a little hole on the bottom of the top half of the carb,its near the edge. I used to have an old one if I still did I could take a picture of it. I can look in a book I have too I think that showed it (petersons guide to the Pinto).


If you hold your finger over that hole after you push t he valve plunger in, the plunger should stay in until you remove your thumb from that hole and let air back in. That way you know its working before you put the top back on.

NM was right too it could be the float or something not cutting off the fuel and raw gas `spilling` into the carb. But its so easy to test the power valve by just adjusting the mixture screw to see if it will get lean enough to cut off. I think you would be more likely to smell strong gas odors if it was spilling.

The last time I redid my carn I just replaced the needle and seat set the float replaced the power valve diaphragm and put it back together with new gaskets. The rest I dont see any reason to mess with. The accelerator pump I can always do later.

As much as we ALL like to complain about emission testing, in this case it prompted you to get it fixed, which is a good thing.  I still hate smog checks though!