Poor idle can be caused by many things, among them vacuum leak, ignition problems, or carburetor problems.
Assuming there is no vacuum leak, and the ignition is working correctly (check these FIRST), we could then turn to the carburetor.
Using a vacuum gauge (setting for highest vacuum), or setting for the "fattest" idle can cause both erratic idle and hesitation from stop. Highest vacuum will always occur when the throttle plates are closed (vacuum is measured below the throttle plates). This forces all of the idle mixture to be drawn through the lower idle port (behind the idle mixture screw), and nothing being drawn from the idle transfer slot (vertical slot just above the throttle plate). The idle mixture screws will have to be out several turns. This causes a phenomena in the intake manifold known as "puddling" where droplets of fuel adhere to the intake manifold (not sufficient runner velocity to pull them into the cylinders). This is a VERY rich condition, and the idle will "hunt" as the mixture actually reaching the cylinders is not uniform. When the throttle plate is opened (starting from a stop) the runner velocity is increased, and pulls ALL of the droplets into the cylinders causing a too rich momentary stall (hesitation), followed by tailpipe smoke when the engine catches fire again.
Solution: set the idle mixture screws leaner, and use the idle positioning screw (on the side, the one that rotates the throttle linkage) to set the idle RPM.
Remember when adjusting idle, an adjustment to a rich engine may make no difference unless the engine is REVed to clean out the intake manifold.
Jon.
