From memory, I believe the cam pushes the butterfly closed at idle and a spring opens it at full throttle. Just the opposite of later model motors. Reason? Lifting the tiller handle also pushes the butterfly closed to slow down without moving the magneto lever. Lower the tiller, and the butterfly opens again (by a spring) and off you go again. Hope I got that right. It’s been a long time.
As for the mark, I’ll see if I can dig up that info. Later….
EDIT: I checked the “Red” service manual and it does not mention the mark. My guess is the one you are looking at is the one.
