Hard start & poor off-idle acceleration

[JerryWang]

Hello! I have a 1967 Chevy K-10 pickup with a 1963 327 V-8. It has an Edelbrock "performer" intake manifold and an Edelbrock 650 cfm 1405 carburetor. I replaced the intake manifold gaskets a month ago, it ran great for a few drives, then started to misfire and was VERY hard to start/drive. I recently replaced the entire ignition system to try and diagnose the problem (new battery, coil, points, plug wires, spark plugs, distributor cap and rotor, vacuum advance unit) and all new vacuum lines. The gasket under the carb was also replaced. All seems to be working fine (no visible leaks in gaskets or vacuum lines) but it still is extremely hard to start. Once started and warmed up, when I go to apply the gas right off of idle it wants to muffle out and die, as if my advance was not working properly. Once in the higher rpms the motor runs almost fine, with a slight lack of power. Backfires occasionally out tailpipe and out carb if accelerated too quickly.. Could I be overlooking something? Maybe a fuel pump?

-Jerry