Need help with tunning my truck

I need some help getting my truck running right. I've got the truck were it will run and Idle but its definitly not running right. It's will sit there and idle ok. I can even rev it a little bit. But most of the time when I back off the throttle it will pop back through the carb. I've tried messing with the idle screws and they don't make any diffrence. I've messed with the timing and it makes a little bit of a diffrence but I still got some problems.

Here's the stats on the motor.
Chevy 350 bored .30 over
edelbrock intake
edelbrock carborator
HEI ignition
New Cap and Rotor

If you guys have any clues or tips let me know.

make sure advance isnt suckin air

Well I got the truck running better. It ended up buying a timing light. Realized that I had the timing at about 2-4 degrees after top dead center. So I reset it to 8 degrees Before top dead center. This solved all my popping problems. so I took it out for a drive. It still wasn't running right. It just didn't feel like it had enough power. So I brought it back home. I readjusted the valves and it helped a little bit but it still needs some work. It feels like it is missing when I try to accelerate. At least thats what I think it is doing. I may be wrong.

The only thought that I had is that it might be that the plug gaps could be wrong so I re-checked them and there at 0.045 If you guys have any clues or insite on what I should check.

I don't know I just figured that this motor would feel more powerfull then what it does.

If your idle screws are not making a difference, you may have some clogged passages in the carb,When you say IDLE screws are you refering to air fuel mixture or actual idle screw? is it new or rebuilt? Thats what was happening on my 64 (and several other rust buckest I have owned).. Check all plug wires, check all ignition leads, make sure you have good clean grounds. Recheck your timing TDC distributor location pointing to one (basically start from step 1 and take your time and retrace your steps..)