This is reference to the hot air type of choke.

• Bad thermostat - replace the thermostat - test by heating water and immersing the thermostat. The spring should move instantly at least 1/4"
• Hot air tube is plugged. It should be hot to the touch all the way up.
• No vacuum in the housing - vacuum supplied to the choke housing is used to suck up the hot air from the hot air tube. Take the thermostat off and with the engine running, blow a little smoke into the choke housing. It should get sucked up through the vacuum passage.