How do you adjust automatic choke on 1966 mustang 6 cly engines?

Those have a spring actuated choke flap, loosen the 3 screws on the outside of the housing, and while the engine is cold turn it until the flap is closed ( barely ), then warm up the motor and observe, as the engine warms the flap will open, the spring responds to warm air. The engine should run in high idle during this time.

The choke should also flip completely open when the gas is pressed suddenly so don't do that when starting cold as it defeats the purpose.