It should fully close the throat, when you fully pull the choke knob out, the plate should rotate to about 75 degrees and block the throat.
You can move it by hand to see what im talking about.
Are you not pulling the knob tully out? It has 2 positions, first one is fast idle and moves the plate almost negligible like this, and one is full choke for start where the throat is blocked.
To start, you pull it out full, and start engine, as soon as it fires, you push it back to first position, it will keep the rpm at about 1500 and you should push it to off fully once the engine is smooth. (Warmed up or you are driving continuously where you dont have to idle again on cold engine)