Automatic Choke System

Throttle is depressed slightly before starting vehicle when engine is cold. Tension of bi-metal spring closes choke valve, placing idle adjusting screw on one step of fast idle cam. As starter is actuated, vacuum is created in carburetor. Vacuum draws fuel from float bowl, through main jet, emulsion tube and out of discharge arm into mixture chamber. Vacuum opens choke valve slightly, against tension of bi-metal spring. Vacuum diaphragm opens choke valve as vacuum increases to a certain amount. As bi-metal spring heats up, choke valve slowly opens and is fully open after 2 or 3 minutes. When choke valve is fully open, idle adjusting screw rests on lowest step of fast idle cam as engine idles.