Originally Posted by USAZorro
It might be as simple as loosening the screw that doubles as the pivot in the bar end just a little bit. Another possibility is that you're missing one of the friction plates (not sure if that's the proper terminology) from the shifter.
Good call. When I first got my bike the barcons were both hard to shift. A local legend, Ed Litton, loosened the pivot screws (actually, he loosened the nuts) just a hair and suddenly they shifted easily, but still had enough friction to stay put.