Sluggish motor?

If you watch closely, every time the Y axis changes direction, the right motor lags behind. How do I correct this?

Make sure it is actually powered. Take off the belts and make sure the pulley is tight and the motor is actually working.

Well, upon further inspection, the pulley was slipping because a grub screw FELL OUT!

I, of course, can not find the little bugger, and even though I cranked it down on the flat, it seems to be slipping with just the one.

I guess I get to buy a few new pulleys to keep as spares!