With the engine cold take off the air cleaner. Open the throttle slightly to allow the choke valve to close. It should close all the way.
Without moving the throttle start the engine. The RPM should be around 1100. See your motors manual for specifications.
As the engine warms up the choke valve should gradually open up. Once up to operating temp, the valve should be fully open.
If it isn’t opening feel the hot air tube that runs from the manifold to the carburetor. It should be warm and closer to hot.
If the hot air tube isn’t getting warm, disconnect it from the carburetor, start the engine and put some kind of smoke close to the opening. The vacuum inside the choke housing should suck the smoke inside. That is how the hot air is pulled up from the manifold.
Take the thermostat off and immerse it into hot water when the thermoset is cold. The spring should move at least 1/4″.
If the hot air stove pipe is missing, or kinked, or perhaps it isn’t getting hot air from the manifold, then consider an electric choke conversion kit. The stove pipes are generally not produced.