I would be looking at two areas that will influence part throttle [cruising] stumble /popping conditions. 1, as already suggested above is the incorrect choice of idle jet. As already stated the idle jets meter fuel for the idle and progression ccts, which by the way is 80 -90 % of most of your driving. WOT is rarely used in the scheme of things. 2. poor carb balance between carbs will also produce similar symptoms. A carb balancer /synchroniser will be your best friend to sort that out.