campy rear derailleur adjustment trouble
 

1st time installer of rear derailleur-2005 campy veloce (medium size) with 12-25 cassette. Having trouble with adjustment, keeps skipping cog 16 & 21. According to campy directions, I make appropriate adjustment and then it doesn't skip cog 16 or 21 but won't shift onto cog 25. Any input would be much appreciated.

Bent hanger?

no
brand new

Start the adjustment procedure from scratch. Disconnect the shift cable and set the outer derailleur travel stop so the chain will shift cleanly to the smallest cog with out spilling the chain outside. Shift the derailleur by hand and set the inner travel stop until it will shift to the 25 cleanly but doesn't throw the chain into the spokes.

Then shift the brifter to the "most relaxed" position (i.e. push the thumb lever multiple times until it stops.). Connect the cable and pull all the slack out. Then adjust the adjustment thimble until the smalles to second cog shift is clean both ways. Then it should shift the entire cassette properly.