You need to start the car cold with the air cleaner off. Press the gas pedal to the floor ONE time, then check to see if the choke really is almost fully closed, just a tiny bit of clearance. There is a specification, but I can't find it now.
I'd bet it's in here:
http://u225.torque.net/cars/SL6/docs/Carter_BBS_Service_Manual.pdf
If the choke plate is right, start the engine and watch what happens on the carb. When the engine starts, manifold vacuum starts to pull the choke plate open if the choke pulloff is functioning. If that doesn't happen, the choke plate will remain mostly closed, the engine will run rich and you'll soon have a black sooty patch on your driveway. Hope that helps.
BC