how large of a carb can perform well on stock 273 commando ?

The Edelbrock on my sons 318 seemed to run a bit lean at Idle. Hard to to keep running when cold. I was going to try different rods to richen it up a little, but the 4295s carb ran so good, we just left it on. His car is an automatic. Sometimes you can loosen the screws on the throttle blades, close them to center them better and retighten. If you wanted to try your original carb again someday. Nice Threads by the way.