Turns out that the cooling flap mechanism is not running smoothly. I suspect of various reasons and I will try to address them all.
1) Long cable with too many curves. I think the original design imposes a way too sharp turn on the final cable attachment inside the cooling tunnel. On top of that, I added 1 turn when I decided to install the lever on the center lower panel. To address this issue, I will drill an eyeball firewall passthrough beside the fuel line on the center channel downwards, directly pointing at the cooling flaps. This will result in only 1 curve on the cable instead of the initial 3 turns. Also, the length of the cable will reduce to a couple of feet instead of 6 feet, thus reducing drag.
2) Cooling flap port rubbing against supports. I bent out a little bit of the supports and now the door is swinging freely. less drag when fully closing it.
3) Cable locking nut not freely spinning. I sanded out the nut hole a little bit and now the wire lock can spin freely.
4) Lastly, dent on the wire close to the cable sheath end. The dented wire makes it a lot harder to run the wire when pulling the control knob. When I cut the control cable shorter, this will be fixed.
https://youtu.be/t6hqRqPp0yc