I dont know the function but the real cover, the black ugly one under the chrome is vented in the bottom tab. The Cobra covers are all one piece and vented as well. It seemed to me the vent hole was larger on the Cobra part.
Again Im no scientist, so I do know what that all does, but after installing the cobra covers some minor decel popping that had been irritating me lately is gone. If the tiny vent holes have anything to do with decel popping, it would seem to me very easy for some of them to get clogged with a minute particle.
I washed all the OEM parts I took off, and they were fairly clean where it mattered but there was enough junk in and around the area the vents were that a tiny piece can easily block the venting process.
not too smart but am opinionated....
It sounds very plausible to me...
I do know that on the small square block carbs that are used on powersaws there is a small vent hole on the side of the pulse pump that is used to transfer fuel to the carb, the cover plate on that has a small vent hole and they tend to become plugged over time with fine sawdust. When they are plugged it definitely effects the performance of the diaphragm that acts as the pump... The diaphragm on the top of the carbs moves up and down to keep the velocity of the air ± constant and so if the vent hole is obstructed it could have an effect on how fast the carb responds to throttle change and may lead to some problems...
Good thought ......