Left to right
Anything affecting only one side and I would guess carb issues. There is an easy 10 minute check. Swap the carbs left to right. Sure it's not a permanent solution but if the poor running follows the carb you know where to look.
It your ignition leads are long enough (or you are willing to extend) you can swap them left to right as well.
As said earlier, do one at a time and I think there is a good chance you will find your problem.