All these automatic chokes work about the same way.
Cold (overnight cool down) start; depress accelerator to floor and let off to set high idle. What happens when depressing accelerator is the choke’s bimetal spring forces the choke plate closed via a rod (not real tight with a lot of force, and not loose enough to allow it to flop) Adjustment of force applied is accomplished by rotating bimetal spring in choke stove housed in manifold, or if electric, turning the black disk that two wires are attached after backing off three screws that lock it down. During real cold (below zero) depress accelerator ¼ down while cranking engine; don’t pump or it will flood; you don’t want to go there.
Once vacuum is present at light off, the choke plate is instantly repositioned from full closed to cracked open about a ¼” maybe 3/16” or so. This makes a rich mixture with enough air to allow engine to run smoothly at high idle (around 1500 rpm) for a short time while heat is building in intake manifold and choke stove to cause bimetal spring to unwind, or if electric choke the bi metal spring is a resistance coil heated by electron flow. A stone cold manifold requires an excessively rich mixture because as air/fuel mixture passes through it fuel will come out of suspension on any cold internal surface leaning the mixture.
As bi metal spring uncoils during warm up, choke plate is progressively opened. During this same time movement of rod connecting bimetal coil or spring causes high idle cam to move progressively reducing engine rpm. This is what happens after startup when one gooses the gas to kick down idle. Pressure exerted on throttle shaft keeps high idle cam from moving, and once throttle plates are opened the high idle cam is free to move as much as the bimetal spring & its choke plate rod will allow. Eventually everything warms up, and returns to normal.
Reasons for this Rube Goldberg choke contraption not to work well are numerous. I list a few common maladies that can be singular, or several causing problems.
Dirty exterior of carb not allowing free movement of various parts, clean using a brush and spray carb cleaner until everything moves freely.
Worn pivot points in linkage and rods causing binding when actuated; cure is to remove the part, and smooth worn area with a fine file. An example would be the rod the moves choke plate closed may bind at its connection to plate causing it not to fully close by its self, but when jiggled by hand will snap shut.
Vacuum diaphragm ruptured, unable to retract device connected to it; cure replace it.
Broken bimetal spring, cure replace it, same goes for electric choke spring.
Causes for braking bimetal spring can be one to many heat cycles.
Electric choke:
No cooling air provided by controlled vacuum leak once engine starts flowing past spring allowing it to overheat and self-destruct. This is one reason not to leave key in on position when engine is not running.
Electrical connections: need full 12 volts not supplied from ignition circuit or coil, but by using a relay triggered from ignition circuit, and good ground. If electric choke pulls off too fast there are thermistors that regulate voltage flow to ground by reading engine temperature to slow pull off.
