'74 Maverick 302 - Low vacuum / Carb / A/C issues

Sorry for not reporting back yet. I haven't had much progress with the Vacuum pressure. Playing around a bit Sat, we isolated some parts, eg the line off manifold to A/C stuff inside, without finding anything. Replaced a couple old T connectors with no result. Sprayed some water around the carb gaskets and some of the connections but didn't hear anything. There so many vacuum lines that I get lost, especially in a couple components on the front of the eng that look like they are getting lines from direct manifold and ported carb. It's a steep learning curve with so much stuff everywhere.

Photos: https://goo.gl/photos/XoUM7SRqvQUw9PHy5

On a cold eng, with idle mixture screws all the way in it will start and run. On a warm engine it will not run. We took of the loosest idle screw and stretched the spring a tiny bit and it feels better now. It's just set at 1 1/2 turns out without fine tuning at the moment. From there we adjusted the timing a bit and got up to 16 inHg. Adjusted to where we were getting 17 but it started sounding sort of like a backfire. Still not entirely happy with the way it runs and also noticed there is some clacking coming from the valves, I think.

We did do some testing inside and I'm pretty sure our A/C problem is the vacuum selector switch. We'll see if Melvin's has one tomorrow and replace it. We were getting vacuum to the switch, but nothing to any of the vacuum motors. So we took out the A/C controls and saw some black stuff in the source port. Can't tell what's in there. Maybe oil or rubber from the hoses?

That's where we are at the moment. Still a lot we didn't get around to checking out. I'm extremely grateful for all the suggestions and tips.

Thanks,
Randy.
Morrow, GA.