I think I'd do it. Reynolds is a major BA suck. Youk is legit and will hit for a significantly better average than Reynolds. I've never been majorly high on Carp and with his injury risk I think he's worth trading for the upgrade from Reynolds to Youk. What pitchers are available on the WW? You'll have a free spot to play with if you make this trade.
One small thing you may want to think about is the fact that Reynolds has actually been running this year and could provide you a few more SBs than Youk. Considering how Reynolds is going to drop your average though, I'd call the SBs negligible.
Carpenter is showing flashes of his brilliance that made him one of the best fantasy pitchers. Also, Youk is good, but doesn't offer the power potential that Reynolds does. If you can lose the BA with him, you will be highly rewarded with the power and steals it appears (so far). I think that what you gain in Youk isn't enough to off-set the pitching the Carp gives or the power that Reynolds offers.