The Main Arm Assembly(#1) is set too low. It's catching on the top pivot(B1) when in the closed position.
There should be a Stop Plug(Sholder Bolt) in one of the holes in the Adjustable Arm(#4) to stop the Main Arm(#1) from drooping too low.
Note the holes, that are closer together, toward the bottom of the Adjustable Arm(picture below
). The Stop Plug(Sholder Bolt) should be in one of those holes.
Adjust the hight of the Main Arm, with the Stop Bolt(Sholder Bolt), so it doesn't catch on the top pivot.
See: Stop Plug. Page 3(Fig.2), right column
Also see: Page 6(Fig. 11)
for Sholder Bolt . The adjustment is explained on Page 6(step #8).