I've just modded another. Here are some pics. The stop is the round post. The actuator arm is painted red for clarity. File so as to increase the gap between the round post and the actuator arm, at the location shown as bottom. The red actuator arm is L shaped near the round post, file the L where it contacts the post on moving out (up in the pic) from pressure on the diaphram.
7.3 KB Views: 898
6.6 KB Views: 861