I worked on a friends FED (nick name balls cooker...long story) and it two 2.250 holes in the back of the scoop to make it run. Before that it was pissed off. I don't remember who it was that told me to drill the holes but it went from untunable to tunable.
We called that "air packing" which basically creates a blockwall of high pressure in the scoop/opening. Drill holes, pressure is released and flow is re-established.
A good filter is beneficial on a drop base. Not so much in a velocity stack, etc.
Carbs like air coming in from STRAIGHT down, not turning corners to enter the venturis. There are test out there that display this.
