Back in February 2009 the club meet at Ken Parker's shop in Van for a session on carburetors. Several of us brought our own to work on. Ken spent the morning walking us through the process of disassembly and evaluation of the various parts to a carb, cleaning and then reassembly.
(Here is a good diagram of how the Model A carb works.)
A very important part of making an 'A' run properly is getting all of the jets properly sized so that they flow gasoline at the proper rate. According to Ken, a jet is measured by using a constant 3' water column, and then measuring the flow of water through the jet for a minute. Ken had his apparatus set up, and all of us took the opportunity to test the jets that we had in our carburetors. Here is an example of a real nice tool. (Note: This picture shows how NOT to use the tool! Holding the tip of the outlet below the bottom of the stand pipe adds to the head pressure and makes the resultant flow too large. The tube must be held so that the tip of the outlet is the same as where it comes out of the PVC fitting.) Ken's was much simpler, made from several pieces of PVC and fed by a slow trickle of water from a garden hose.
Ken showed us how a jet that is not flowing the proper amount can be fixed, either by very slightly drilling out the hole, or soldering the hole shut and re-drilling a smaller hole. But you have to have a set of small drills: a set for sizes #61-#80 is available at most tool-supply houses. (Do a Google search on "drill index 61-80" for a wide selection.)
Another important part is making sure the passages in the carb are clean and will allow gas to flow. A small light is helpful. Ken was using a small LED light but suggested the fiber optic adapter for a MiniMagLite (See here.)
After, I did a bit of 'net searching and came across this site:
Ken showed us a paper worksheet (many pages!) that he has found useful when overhauling a carburetor. It used to be available from the above site but seems to have been lost. I tracked the author down and with his permission here is the worksheet. You can print it yourself.
Here is another good reference for flow rates. Note that this reference says that Ford originally specified flow rates under 37-1/4" of water, but most everybody now does it at 36".