Pull one spark plug wire at a time (carefully) and listen for the reduction in RPM. The cylinder which does NOT produce any change when the wire is pulled...is your miss.
Given what you've described here, I'd go looking for a vacuum leak. Could be that something is leaking, running way lean, when the engine is cold. Leak closes up once parts heat up and expand. Spray some carb cleaner (or flammable liquid of choice) around the manifold, carb base, wiper connection, etc. Listen for it to smooth out. Some folks prefer an unlit propane torch, but you have to disconnect the fan belt for that to work very well.
Having said all that, I would expect closing the choke to improve the miss....if a vac leak were to blame. It's an easy and logical place to start, anyway.
