1971 MGB engine runs eratic

Recently overhauled engine and replaced timing gears and chain. Points and timing are set perfect, all cylinders firing, compression good, valves set by book. Cranks good, idles good, but dies down when pressing accelerator and spits and pops out of carbs.

updated 4/7/2010
Hello, oil dampers are at correct level, and have installed new coil. Ignition output is good. Although, I did notice one thing in parts manual that does not list in my MGB manual. Parts manual shows 2 shims under middle rocker stands. Didn't noticed if my engine had them when I tore it down or not. I do have the valves set at 15 cold. Could the middle shims not being there be causing my problem?