Hard cold start- lack of fuel- UPDATED

I'm trying to figure out a situation I've had for years with my '67 Barracuda 273 2bbl.

It has developed a hard starting problem if it sits overnight or longer. The apparent problem is lack of fuel in the carb. I pump the accelerator to set the choke and it will fire briefly, then die. Takes lots of cranking to get it to fire again, after which it runs normally. If I first pour some fuel into the carb, it starts right up, then dies, restarts with minimal cranking. If hot, it takes some cranking and starts with very slow idle,becoming normal after 10 seconds or so.

It used to start right up with only brief cranking, cold or hot. Has a Holley Economaster carb, installed 25-30 years ago, never rebuilt.

Electronic ignition (Mopar), new plugs (Champion RN14YC), new mechanical fuel pump, new fuel filter, new air filter, new fuel gauge sender, all-new rubber hose in the fuel lines, all made no difference in starting. Engine runs normal temps (new thermostat), fuel line and fuel filter stand off from engine and manifold. Battery cranks the car properly (fourth replacement battery for a JC Penny Lifetime Battery purchased 38 years ago!). :scratch:

Thoughts?