I have a 1998 Honda Magna with a rough running engine. It idles rough at idle and runs rough as in "surging" during low speed operation in 2-3 gear. I have overhauled the carbs with new stock parts including the main jets,slow jets, float valves, o-rings, gaskets, etc. followed by a carb sync. after re-installing. I did not touch the vacuum chambers or the pilot screws. I can here a "popping" from the exhaust at both idle and at cruise, although the bike runs well at 3000 rpm and above. The engine almost sounds as if I'm running on only three cylinders (except during acceleration), but all the plugs (new) appear to be firing.