Classic/Antique Car Repair: 4bbl on Caddy (500 8.2 L), partically, custom exhaust

Question
Is there a diagram or step by step to adjust a Carter 4 bbl carb on a Caddy 8.2L?  The longer it sits, the longer it cranks before starting. When runing 30 mph, after a few miles it stumbles and quits but pumping the gas gets it going. At interstate speeds, it has lots of go, but then begins to stumble and runs rough. It has new electronic ignition, vacuum checks, new gas pump, Edlebrock high rise intake manifold and custom exhaust. Local shop tried different length rods on carb, idle adjust, even messed with the timing but not luck. When first put on would pull 550+ HP. Starts fast after being run a few minutes. Any ideas? Engine was rebuilt to original spec.

Answer
HI Henry:
This one is a tough one. It you are sure your timing is correct. Check the fuel filter or fuel tank. You may have garbage in the tank or filter causing the problem. Also, be sure it is not foul plugs when you gun or a partically stuck automatic choke.