Needing some help with a friend's 56 Vicky. It backfires through the carb on acceleration like it's running lean, but the plugs are dry black indicating rich. I rebuilt the carb which is apparently from a 57. I also installed a Pertronix and found the dizzy is also a 57 type as the Pertronix is different for a 56 dizzy. The car ran good before Winter and when he took it out of storage it ran like crap. While working on it, it ran out of gas so the gas in it is new. To be safe I installed a new filter. I also installed a new distributer cap, rotor and plugs. I'll install wires tomorrow as these are 17 years old and feel a little brittle, not cracked, but getting there. I really don't think it's ignition and definitely seems like the carb, unless maybe a timing chain? I've never had a timing chain go bad. I've built a bunch of engines and always put in new Timing chains or gears so don't know what symptoms a bad one has. 
Here's what I have so far:
Engine: 292. He bought the car 17 years ago and knows nothing about whether it was ever rebuilt. He just cruises and is not hard on it.
Trans: FOM
Carb is Carter 4bbl AFB
Fuel pump puts out 3.5 psi while cranking it over.
Engine vacuum was around 8" but after new intake gaskets its now about 15. (Still low)
Vacuum advance works easily with a Mity Vac.
Compression test ranged from 85 to 115 with most around 100-105. This isn't real good I know.
Initial timing is 7* advanced at idle w/ vac advance disconnected and plugged at carb.
Starts easily and once you get past the carb coughing it revs well. Driving it is another story. Coughs a lot getting to speed.
Mixture screws were having zero effect and could be screwed in all the way (gently) and the engine still runs just the same. To me this would indicate running rich or flooding over. I've been working to get the idle as low as possible so as not to be running it in the transition stage. After adding the Pertronix and replacing the intake gaskets I can get some change using the mixture screws, but not what it should be at all. If I screw them in all the way it will kill the engine now, but it dies slowly not like you'd normally get screwing them in where it usually kills it fast.
I've rebuilt and been through the carb at least 3 times. I've sprayed carb cleaner through every hole, jet or opening and watched for it coming out the other end. Then followed that with compressed air. I've rebuilt a lot of older Holleys and do have a clue about carbs and this AFB, though different, really isn't a hard rebuild. To be safe I followed step by step using a Carter book by Dave Emanuel. I've also used other info like the Ford manual and whatever else I could find. I set the floats at 5/32" like the Ford manual and carb kit instructions say, but everywhere else people say set them at 7/16". That may be generic for Edelbrock carbs as they are almost the same. That is a lot of difference though for a float setting. I figured the Ford setting should be right for this particular carb.
I'm sorry this is so long, but I figured if someone was to take the time to consider what's going on, the more info the better.
Thanks in advance! Roy

Life isn't about arriving at the end in a pristine, well preserved body; It's about sliding in sideways, all clapped out, yelling "What a ride!"