Exactly what Kit said that is the way the system works. The side flapper is to give the engine a shot of extra air flow when the throttle is cracked open. Same principle as the Ram Air system, no vacuum doors open, vacuum doors close.
By the way do you know the build date on your 73 Q code? Always a discussion on the 73 Q codes coming with that air cleaner and Ones that did not. Mine came with the chrome top / side flap / door, built 12/22/72. Just currious.
Hello FastE; According to my Elite Marti Report, my "1" of "1" 1973 Mach 1, last serial numbers being 15939 was built on April 24 1973, 20 days behind schedule.
Purchased car from original owner's widow. Car was sold from a Santa Clara, California Ford Dealership ( Dealership still in business) & car NEVER left the area.
Car was 100% STOCK as delivered from dealership, when I purchased it & came with a OEM 351c 4V air cleaner, Ford Blue in color, NO chrome lid.
Being a garaged California car, the body is 99.99999999999999999% Rust Free, only rust is under battery tray ( more like corrosion than rust) & a few pin holes in the back seat floor pan.
In the process of installing a new interior carpet kit, I found the original Factory build sheet under the passenger carpet padding.
Car has NEVER been hit & retains ALL factory sheet metal.
Was SERIOUSLY in negotiation for an original owner Highly Optioned 1969 Mach 1 "S" code ( 390ci engine) 4 speed located in Kansas. Deal fell apart at $18,800.00 ( STILL KICK MYSELF over that one!!!) when I happened upon the 73 Mach 1.
Only found out about it being "1" of "1" after purchase.
Was not a huge fan of the 71-73 Mach 1s, BUT....The car is definitely growing on me!!!
Recently purchased a Factory Ford dual exhaust rear valance & installed that, along with the flapper door air cleaner.
Engine still is 100% correct ( except air cleaner) & still has the dual point, No vacuum distributor, factory carb/intake/exhaust, etc,etc.
Finding a replacement accordion flex hose that runs from the air cleaner snorkel to the cold air intake piece was akin to finding a Unicorn in a field of 4 leaf clovers.
Shifting from 1st to second with any amount of throttle, Instantly produces a "Nice CHIRP!!!", as the car has ALL the Goodies in regards to Comp Suspension/Traction-Lok differential/351c 4V ( believe motor is a 4 bolt)...Mark