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What sort of adjustments are made by the expert builders to make a carb a lot better etc?how does a flow bench work?I am not asking for secrets,its just we are so limited to what we can do to carbs I find it interesting as to what is physically done to the carb etc.

A lot of it is that a pile of carbs are all flowed and the best parts from each of them selected. Then the bowl is radiused, the jets are shaped to look like a bullet and a few other tricks are done to increase the flow. I was told once by an engine builder that they may flow 10 different tops and ten different bottoms and have 1 or 0 "good" ones found from that.

Smazzy is correct in that going through multiple carbs parts with a flow bench is the biggest part of getting a good carb. There are also a lot of labor intensive items after that. The throttle butterfly and shaft are taken to minimum specs, screws replaced with flat heads, ec. (and a few more tricks). Without a flow bench and then dyno (or lots of track time with proper equipment (02/EGT,etc.) You can only guess at what you have. For comparison sakes, I have seen race prepped carbs that flow from anywhere between 104 cfm and 117 cfm (at 28in of water pressure) The HP difference at 6000 rpm between a 104 cfm carb and a 117 carb is big.

There is really no simple tweaks that can be made on a carb at home to insure that your flow is better or mixtures are correct. The only possible exception is making sure that you do have a race venturi (which I am sure you do) and that the a/c jet is shaped more aerodynamically. Even after those changes, proper a/f mixture has to be adjusted with the above tools.