Before the idle can be "smoothed out," it's important to have valve lash set to proper clearance, points gap and ignition timing correct. Of course, one wants each float set to proper level and the throttle needle clips in their proper notch. Then adjust each cable so all 4 slides open at same time (allowing approx.1/16th"+ cable slack) and turn each throttle slide adjusting screw so the screw just touches the slide. Then turn the throttle slide screw another turn. The engine should idle fairly smoothly, but likely will not be exactly right on. If idle speed too high or too low, turn throttle slide adjusting screws in or out accordingly for idle speed of approx.900 rpm. The final adjustment is setting each air screw to standard position. This adjustment should be completed before starting engine. The air mixture screws need to be synchronized. The best way to synchronize all 4 air screws to set the idle mixture is using a CO analyzer. The 2nd best way is using vacuum "mercury sticks" or actual vacuum gauges. Beyond these methods, without an experienced ear and a feel for individual exhaust muffler outlet pressure, it's nigh impossible to get all 4 idle mixture settings the same. All of this is negated if the carbs are functioning with worn parts, such as worn float needles, worn throttle needles, worn air mixture needles, cracked rubber inlet tubes, etc. This is also assuming the valve seats, stem seals, guides and piston/rings are in good condition.
