there are several reasons for not getting full operation.
Rusty's example is one that can happen without care in the setup: Make sure that the disk is installed with the actuating lever arm in the correct cavity--the slot. added on edit: the "correct slot" issue is really a problem for installing the ACB (Adjustable Charge Bar).
Another common reason was called out here, too--having the hopper retaining nuts (screws on the older hopper versions) screwed down too tight. added on edit: and, make sure that the hopper is oriented properly--it should not obscure the disk / bar drop hole.
Don't overlook worn components: components such as the elastomer wiper (on the Deluxe version), the disk, or the ACB can also wear down. This wear can contribute to leakage / buildup, and some friction in the operation.
Make sure the actuating arm slot and screw are cleaned intermittently--fine powder, as editingfx noted with AA#5, helps gum things up.
Finally, clean the PTED as well, particularly if you've been using it awhile.
Jim H.