If you leave too much clearance when you adjust the FD low limit you may run out of cable pull at the other end of its travel. Be sure that the high limit screw is not too tight, limiting the derailleur stroke. Also make certain that the height and rotation of the derailleur is correct.

Finally, if you are really certain that you actually have too little pull, try attaching the wire the "wrong" way to the clamp bolt, going underneath the little tab. This will shorten the lever arm and cause more derailleur travel per lever click, although the force needed will increase. This might buy you enough travel. It costs nothing but a little time to try it.