The rig is almost balanced..
Before going into detail of balancing, first of all lets understand how this rig catches a carp. When we put feeder rig in water, small fishes attacks the bait and in that process creates lot of cloud around it. Attracted by the commotion of feeding and attractive smell of the bait, big fishes comes to investigate and fish like Catla, start sucking the cloud around the hook. Now our setup should be such that as the fish sucks the cloud of particle, the hook should rise and go in the mouth of that fish. It is at that point that the weight of feeder comes into play and the fish is hooked.
Now balancing the hook part.
1- Tie the hair rig as shown in the picture posted above.
2- Put the tied rig in water, the cork will be floating and the trailing length of braid will sink in the water.
3- Add a split shot on the braid line below the hook.
4- Put the rig again in the water. If the weight is sufficient the cork will sink in the water, otherwise add some more weight.
5- When the cork start sinking, observe at what speed the rig is going down.
6- The balanced rig is where the rig sinks very- very slowly and the split shot rests on the bottom. Adjust the split shot that the length of split shot to the cork is almost equal to the diameter of ball bait. Experiment with the length from feeder to the split shot. As a basic rule, the length of feeder to the split shot is twice the length between split shot to the cork ball.
Hope I had made my self very clear.