My 68 XR7 GT has been sitting a while fixing the electrical issues and now it can start but with some work. It now hesitates and stalls out unless it has been warmed up for more than 10 minutes. I am using the original 600 cfm carburetor with proper automatic vacuum advance. The immediate thought was the accelerator pump which is now replaced. It now starts better but still hesitates. Could it be the check valve sticking or another minor adjustment? I use 91 or 92 octane non-ethanol gasoline which in the past ran fine in the rebuilt 390 GT.
Not very common but I have worked on cars with the pcv valve installed backwards or stuck open . A gigantic vacuum leak that can be overcome with carb adjustments but when you hit the gas or drop it in gear it just can’t keep up and dies
I would nspect the spark plugs. Fouled plugs can can act like that and it’s easy to eliminate as the problem.