The housing to the left of the carb as you're looking at it from the front is the auto choke adjustment spring. It has a black cap with "hash" marks on it, from rich to lean. Loosen the screws, but don't remove them. Turn the black part of the housing to center and then go 1 notch rich. As you move the housing back and forth you should see your carb. flap moving when cold. If it doesn't you might have a broken spring. This would cause the choke not to set. Move it to one notch rich when cold and then try to start it. If it doesn't and you now think the spring has failed remove the black plastic housing to determine if there is a broken spring. If not, the mechanism internal to the carb. might have failed.