Page 541 of the manual has it! "Automatic Choke (Vacuum Kick) System (Fig. 7) The automatic choke provides the richer fuel-air mixture required for starting and operating a cold engine. A bi-metal spring inside the choke housing, which is installed in a well in the intake manifold, holds the choke valve in the closed position."
You are getting closer, but that sounds more like just the carb choke. The system we are talking about is on the air cleaner and the intake manifold like Keith posted