That's because you can't......
Here's a really good thread on tuning. Tom Vaught was an Engineer at Holley and quoting Shrinker so would know more than the experts here. Start at post #150
SOME HOLLEY CARB TIPS PONTIAC forum
Some key take aways: testing was on a tunnel rammed 400 ci race engine.
"When I say to you guys that a particular engine hasn't got enough vaporization that is what I'm commenting on. How it looks inside the cylinder is like this, the AFR at ignition time is leaner than the average of the cylinder, lets say the average is 12.8 but at ignition time the AFR around the plug is AFR 14, the flame is going to grow slow and some of the flames energy is going to used in vaporizing the fuel thats not gas yet. So the flame kernel doesn't generate enough heat and you dont get a TAN plug, you also run the risk of extinguishing the flame if turbulence is poorly directed.
The burn time determines the peak cylinder pressure. Its the peak pressure that is one of the principle determining factors for the production of CO into CO2. If its not high enough you wont get the conversion underway so the exhaust contains high values of CO. If the CO is produced with a high oxygen consumption then the exhaust stream will be low in O2.
Now a WB theorist will tell you that the WB will use the unused O2 to convert the CO into CO2 etc and complete the burn to perfection and report a result. Well that's correct but the reality of this type of burn is that the O2 is used to make excess CO and forgo the conversion to CO2 because it just didn't get hot enough for long enough. This type of burn is far from correct as the theory books only want to consider.
There isn't the normal correct balance of O2 to CO of a rich burn. The CO2 levels are low and the WB catalyst needs the CO2 to break it apart and get some O2 to reform the CO to CO2, the reaction of which is O2 neutral. So the WB has to get the O2 from the outside air and that causes it to report a high O2 requirement thus richer than truth."
(The Late and Great Bruce Robertson AKA Shrinker!)
"So in simple Tom Vaught terms:
Learn how to read Plugs and don't trust the Air/Fuel Meter to be the Final Word on the Air/Fuel mixture going on inside the engine.
Tom V."
"Some can read them better than I can, but I am ok on the electrode and a bit down on the insulator. Shrinker was a PRO, (I was told) on that deal.
But again I am just posting suggestions to this thread (Not making assumptions based on just one piece of information from one piece of equipment.)
Tom V."
Oh and Tim let me know when you're Carbs are on and tuning Pro Stock engines I'll gladly sit at your feet to learn what you have figured out.