The pop-up stopper in an American Standard bathroom sink won't pop up
far enough. The water will drain out eventually, but there's only
about 1/16" (maybe less?) between the o-ring and the mouth of the
tailpiece.

I've fiddled with the rods, etc under the sink, but that doesn't seem
to help. Even without the linkage, I can't move the pivot bar far
enough to lift the stopper clear. If I loosen the nut that holds the
ball and pivot bar to the tailpiece, I can just get the stopper high
enough to drain quickly.

Is there a secret adjustment I don't know about? Did I get a mixed
bag of parts from the plumber's spares box?

Thanks.