Home made carb balancer : go buy 20m of clear tubing ,5-6mm dia, cut 4 equal length peices , 4.5m each , not exact but enough to reach to the side of the car , attach these 4 tubes to a flat board and join all off them together at the bottom. then fill with car oil to half way up this meter long board ... then connect the 4 open ends to a vacum port on each carb, not sure if webers have them ? maybe the manifold does. then when you run the car the level of oil in each of the pipes should be level , if one is higher this port has a high vacum , and you can adjust. cost be about 5 quid to make