There is a small vacuum hose leading to a very small canister on the passenger side of the carb, with a lever that connects to the choke plate - thus I thought it was a vacuum operated choke of some type, but I must say, it really seems to have no control over this plate, even though the two are connected. The rod end off the canister is in a slot on the arm of the plate, and just seems to slide in this slot with no real effect on the movement of the plate.
That is called a "choke pull-off". When working right, the choke flap is 100% closed if you push the accel pedal down and DON'T start the engine. Then, as the motor starts, that vac can pulls the choke blade open just a little, so it does not flood.
Edit: You can check the vac can easy; Put a long vac hose on it and use your mouth to see if it is leaking, or if it actually will open the blade "slightly".