Revving at stand still doesn't mean much, since then the engine needs only food (air&fuel mix) for running itself. On the road the load grows exponentially with speed due to drag/air resistance, but even at walk speed there is the weight of the bike and rider + all the moving components friction added to load = engine hungers for way more food. So first I would check if the slides are worn out and jiggle loose and/or have some wear notches, which could cause them to tackle when the air flow grows and pushes them towards engine. Second - are you sure that the jetting is correct, since it sounds like you haven't ran at dyno? Third, check the pressure hoses, I understood that they're CV carbs.