Toro 11-32 (or 56170) carb question

I'm trying to resuscitate this mower that's been idle for the last 6 or 7 years. While cleaning out the carb/old gas I noticed there is a threaded hole in the bottom of the carb, near the choke plate. Should this have a screw of some kind in it? I don't see one on the parts diagram.

Here's a pic with a brass screw threaded into the hole, from the bottom. The float bowl isn't pictured but would be to the left of the screw.

http://i213.photobucket.com/albums/cc93/tharba/IMG_1905.jpg

Thanks.