Dude that is some outstanding footage!
Yes that flap is called something like the "secondary air valve", and it should be opening when you are into the secondary. It lifts the needle out of the jet for your secondary fuel. When the choke linkage is in a certain position it is disconnected and won't open. I would take the carb off and play with things until you see what makes it operate or not.
Probably has to do with the fast idle cam stuff. FYI you can take all that off if it's not going to work properly due to wear or damage and it will do just fine.
