IIRC the shorter stroke was in the 766.The valve was longer by that 1/4"I have had experience with this but it has been some time and my memory isan' what it used to be.I have an early 2200 arm with the protruding link rivet and the 3/16" pivot pin hole.. the 2200A013.This arm needed a wide spot in the middle if the pump tube slot to allow the protruding rivet head to pass thru.It has the 2 5/8" dimension.As do the 2200B013, which have flush rivets and 7/23" pivot holes.As for the pump spring back, allow the arm to be open after pumping a few times, and opening the arm, then pull the trigger.If you get a really week pop or no pop at all, I would suspect the check valve in the valve itself.May be new, but could still be bad........
One other common mistake is instilling the valve with the transfer hole on the bottom and not to the barrel port hole
I have seen a situation in Daisy pumpers in which the chamber seal (check valve) accepts 1 pump and no more.Additional pumps just remain in the pump itself and the pump arm will spring back rather forcefully...That condition is caused by too much oil, causing the chamber seal to seal tightly to the pump walls......I have never witnessed this in Crosman pumpers, but something is causing your check valve to stick open or freeze shut......There just ain't much else to it.