I have a set of Campy Bora Ones. Im installing them on Willier Cento Uno. with the limit screw backed out all the way the chain will not go up to the biggest 26t chainring. I'm using a full Campy Super Record 11 group. It

Campagnolo is no more difficult or tricky to set up than SRAM or Shimano - it's just that mechanics see less of it so
a) don't bother to get trained in how to handle it hence
b) make more of a meal of it when they do see it
c) don't like to say "I don't know" so then tell you it's a bit tricky ...

The most likely problems here are, as Coachphil says, cable tension, or possibly the rear hanger not adequately tight to the frame, the RD not tightened correctly into the hanger (beware it's aTorx key not an allen key), the rear hanger mis-aligned or the H screw mis-set - it depends what the OP means by "won't go into the 25".

If it simply that the OP runs out of clicks before the RD is able to "try" and engage the 25, the chances are that at the other end of the RD travel, the limit screw is mis-set (move one and you have to move both by the nature of how a RD works, to get correct limits set) and insufficient cable is pulled through, so that two clicks on the lever are being used to go from the 12 (say) to the 13.

The solution is to start from scatch with a full installation of the RD, or, as seems to be indicated by the nature of the post, if the OP is not a confident mechanic or is not conversant with how to do this, the bike should go into a Campagnolo ProShop. He can find his nearest ProShop by going to www.campagnolo.com and searching under the ProShop tab at the top for his country and region.

HTH
Graeme
Velotech Cycling Ltd,
Campagnolo main UK SC ' Velotech Mechanics training to national standards

There are a number of possibilities for this. First check to make sure of your cable tension, put the derailleur in the smallest cog and see what the tension is like, is there a lot of slack? then you need to re-tension. I would be reluctant to have you try too much else with these components, better to take the bike into your local shop and have the mechanic look at it. these parts are fairly expensive and none too fun if you break something. Campy can be tricky especially the 11 series and should be done right.