1953 CJ 3A Low Idle Problem

I don't know as much as Scout about building a WO Carter carburator, but I've had vacuum leaks. I'll just describe a few problems I've found and let you look at yours in a similar fashion.

Number one are loosening nuts holding the carburator tight and sealed to the thick insulating gasket under the carb. I put star washers under the nuts to stop this.

Number two was dirt/rust in the float bowl plugging up the jets and idle circuit. I pulled the carb, popped off the top and cleaned it out including the slow speed circuit jet. Carb clean spray, air, and remove the mixture needle and clean the circuit at the same time. Make sure and count the turns up from the bottom that it's adjusted at. If you find allot of junk, maybe install a filter to help stop this. 

Number three, check that your intake manifold gasket is still good against the engine block. Spraying brake clean around it will sometimes show a leak by changing the idle. This may or may not work for you. A good visual exam and checking the nut tightness that hold it is good. I've seen them crack the casting also. 

Number 4 was a leaking vacuum hose leading to the vacuum wiper. (you may not have this since you say you removed stuff) Wiper motor itself leaking too.

Number 5, if you have a bad vacuum advance diaphram on the distributor (If you have that type)

Number six is as Scout says, worn carburator throttle shaft leaking by. 

Number seven that I just discovered this summer, the cap and gasket at the bottom of the carburator well the slow speed circuit jet is inside of had come loose and was sucking sir. It's located on the front of the carb at the bottom of the long skinny jet. 

Hope you find it, Oilly