Wow. I had no idea that thing was inside there! Good catch and thanks for the tip!
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Out it goes. And back to the bench I go.
Here's the quick results (corrected flow data).
Carb + air filter, with black insert = 17.2 CFM
Carb + Air Filter, without black insert = 18.4 CFM
The black insert costs you 1.2 CFM!
Carb + air filter + orange filter cover with black insert = 16.8
Carb + air filter + orange filter cover without black insert = 17.6
So installed on the saw you gain back .8 CFM (the cover still has a detrimental effect)
I retested the carb+filter_cover with insert to compare to last night and I am within 0.1 CFM so the tests repeat well.
I am definitely removing that part from inside my air filter! I will likely machine a spacer for the stud to prevent collapsing the air filter when I tighten the cover.