Hot idle valve is under that tin plate held on by two screws.

http://www.slantsix.org/forum/viewtopic.php?t=61387 In that thread a carb with jet 120-429s was rebuilt. Very few carbs used that jet,posted the sheets, about half used the hot idle valve mentioned in that bulletin. The metering rod and jet were replaced with leaner set up, ran better, Wonder if the carb in that thread had a hot idle valve?