Classic/Antique Car Repair: holly 4160 4 barrel carburetor on a 72 chevelle, barrel carburetor, vacuum advance

Question
hi there. im going to give you as much info as i possibly can, and if you could give me a few answers in order of most likely to least that would be great. a couple of years ago i bought a 72 chevelle that was in need of complete resoration there was only the shell of the car when i got it. i have put a 350 small block bored over 50 thousands and a 400 hundred turbo transmission. the cam is by no means a racing cam but isnt stock either. the problem comes when i try to put a load on the engine. the car starts up fine and idles good when we adjust the idle screw, foat bowls and there is another screw, with one on each side of the carb not sure what it is called but it is some kind of idle screw because when tighing idle drops and runs roughly. while the car is idleing good i would put it in reverse or drive and it imediatly bogs down and runs roughly.i try to give it some gas and it dies. we got it to run better when we advanced the timing to about 4 on the timing marker, but when we do this it idels much too high when in park and still bogs down when in gear just not as bad. the specificatons for the engine say to time it to 8 and for a 72 chevelle with a 350 it say to time it to 6. im not real sure if the problem lies in the timing or the carb or both, but hopefully i gave enough info that you can possibly figure something out. thanks alot

Answer
Ok. Check you vacuum advance (or electric) for proper operation to advance timing instead of adjusting manually.
Is the accelerator plunger (diaphram-HOLLEY) working correctly and check ball free?
 
Does having the choke of half way solve the bog?