Black knob is your idle adjustment !!! The rubber hose it appears is your vacume line to open petcock so fuel will flow to carbs. When the carbs run dry it takes some cranking to open petcock to get fuel flowing again. If your tank is not venting properly, fuel cannot flow. Ck out POOGS!
04-3,200 miles bought July 2011 with 928 miles. Loaded with acessories to many to list here, see my albums for more details! I also make a custom tank bib specific for the 750 if anyone is interested, ck my albums for some pics.