340 fuel/ignition issue?

Sorry, pushed wrong key.
Continuing..
so make sure your base gasket covers all openings in the carb base. Any leaks in [1] or [2] cause the strange problem that you are having.
[3] Flooding. Run engine & shut off. If it is flooding, the boosters will drip.
[4] AV linkage rod. I should have explained it better. Make sure the AV moves freely from closed to open, no binding or catching.
[5] AV 'kick'. I like 0.060 - 0.100" for performance engines. Gently push in the dashpot plunger in with a flat blade screwdriver. The back of the AV rests against a projection on the air horn; it should move the distance listed. Bend the rod to get the measurement.