Mechanical fuel pumps are far better at pushing than they are at pulling. Any restriction introduced upstream of the pump greatly reduces the pump's already-meagre ability to suck fuel from the tank, and can tend to introduce bubbles in the fuel due to pressure differential between the restriction and the pump.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

found out what was causing the problem - it looks to have been a big vacuum leak. It was being caused by the little exhaust manifold attachment block on the d-side of the manifold just below the intake. It has a vacuum pod on it, and apparently with vacuum applied, and hot, it caused a vacuum leak, which made the engine run completely crappy. Not sure what was causing the leak internally, but I capped the port for that pod and the problem hasn't come back yet, even after repeated hot-off-start cycles. I thought it was a vacuum leak between the intake and exhaust manifolds, but I got a good seal there (checked all mating surfaces with starting fluid - no changes).
So, with all the emmissions stuff on top of the engine I'm not completely sure what capping off the port and plugging the line does (it's in the book I just haven't searched it out yet), but it's running good...so as far as I'm concerned it made the car run lots better . I'll drive it this way for a while and see if anythign else creeps up.

It does still seem to be getting air in the fuel system, but apparantly that isn't a show-stopper yet, and I will be bolting in a fresh pump and upgrading the fuel lines soonest, but for now it looks good to go.

Also, apparantly the carb I got is off a '80s-ish 318 - it took a while to find the correct rebuild kit, but it's functioning great and runs a lot better than the old 1bbl. So that's good. A buddy of mine in our Mopar club had the parts including the air cleaner (looks great in there now ), and I'll have to post a pic of the linkage I fabbed up. It's a bit primitive but sure works good, even kept the 1bbl throttle cable.

I didn't change the exhaust manifold or exhaust pipe at all - not going for big power, just need a good commuter .

Really appreciate everyone's comments and recommendations.
- Sam

You're describing your EGR (Exhaust Gas Recirculation) valve. It should not have vacuum applied except under part-throttle, road-loaded conditions. If it was being opened by vacuum under idle conditions, it was not hooked up correctly. Got your factory service manual yet?

Have you bypassed your OSAC valve yet?
Probably made life interesting trying to hook up the choke.
The 2bbl-equipped engines used the same exhaust manifold as the 1bbl-equipped engines.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.