I changed all the cables. I used 1/16'' coated cables instead of the 1/8'' that came with the system. The 1/16'' is much more flexible and it now works really well. At first I didn't like it at all and I've noticed that the guy who sold it to me didn't install it properly.
By the way, adjusting the cables is very easy. Just use a 1/8'' sleeve (me it is 3/32'') and make a loop with the cable. I also thin that it is possible to add weight to it even if they say that we can't. I will try it if i can find other weights.