I once tried to use two different quill stems I had bought from a swap meet and couldnt figure out why they werent tightening enough. I eventually discovered both the stems I had purchased came with mismatched wedges. That is to say, the stems were clearly marked 22.2, but the wedges were slightly narrower, obviously meant for the somewhat obscure 21.1 size. Is it possible that your 25.4 quill stem, which isnt the most common size, has a slightly undersized wedge with it? Maybe one meant for the more common 22.2 size? (If you bought the stem -new- I suppose this possibility isnt possible.)