When the warm air door opens, it allows the warm air to enter the carb instead of the cold outside air. In the winter of 1973-74, I was stationed in upstate New York and the temperature got down like 15 deg below zero and I had left the Shaker cold air doors open. Needless to say, when I got up to about 50 mph, I started having problems but as soon as I hit the cable to open the warm air door, the problem with the gas freezing went away. I learned it really works.
Terry