When you say “fully on” do you mean that the brake lever pulls all the way to the bar, or that the caliper arm is hitting its end stop? If the former, the cable may be too slack, if the latter, it may be too tight. You should adjust the cable tension adjuster to the point that the caliper arm just starts to move off the stop with the brake lever released. Also, try turning the caliper arm tension up all the way and retensioning the cable – this might help take some of the slack out of the outers.
Also bear in mind that the termination of the outers just as important as overall length. Make sure you’ve got a nice clean cut at both ends.