my best throttle response speed with the CVK carbs was drilled 3mm and the stock spring and the shrouding for the atmosphere side of the diaphragm removed (sort of like porting the carb).

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter