Sputtering and popping issues

I have a 63 Dart with a 225 slant six. Car was on non op since 2007. Did a tune up and oil change, took carb apart and cleaned up and it ran like a champ. All of a sudden it developed a sputtering problem and pops out the carb. Car wont accelerate and dies when stopping at an intersection. We put a new fuel filter on and cut the old one open and there was NO debris in the filter. Getting 4 lbs fuel pressure while cranking. Runs fine one time and then all of a sudden it starts all over. Happens when cold or hot. Timing set at 2 degees BTDC per Chiltons Manual. Mixture screw at one turn out.

Help, any suggestions?