There is a little plastic cover on the passenger side of the carb. Loosen the screws that hold down the metal retainer and you twist the cover back or forward depending on if you want it to be more open or more closed. There should be little marks on the cap to indicate more or less.
I got sick of screwing with the auto choke on my 2150 6 years ago and ripped it off and put in a manual cable choke. The cable cost 6 bucks at checker auto and the rest was just putting it in and making sure all the vaccums were plugged.
I ran the cable through the fire wall plug, mounted it to the screw hole mounts for the old choke on the side of the carb, ran the cable through the old choke access hole on the airhorn of the carb, and then attached it to the choke plate. It took a little trial and error, but now I controll the choke, and it's much eaiser.
If you have any old, gas powered weed eaters that don't work, you can take the little swivel attachment that holds the throttle cable to the carb for a little swivelly attatchment to the choke plate instead of bending the wire over. But, bending the wire work well for me for years.