Ok, another good test is to see how well the fuel flows from the tank to the carb. When you first try to start the car put it on the starter box and turn the engine over without plugging the end of the pipe. If there is a good seal all thru the fuel/exhaust system the fuel should start to flow to the carb without having your finger on the stinger. If this does not work try to put your finger over the stinger for just a second so the fuel gets like half way to the carb, then pull your finger off the stinger. If the fuel flows back toward the tank as soon as you remove your finger there is a leak of some sort.

Another thing to look at would be the header. I have seen tiny cracks in the header cause very erratic idles. generally if the header is cracker you will see some oily dirt buildup on the header it's self close to the crack. The crack it's self will be very hard to see but once the header is up to temp and running that aluminum expands and will cause a loss of pressure which will not push to proper ammount of fuel to the carb.