Help! idle mixture screw location
 

first thing's first. it's an 83 RX7 - stock everything - nikki carb.
so, im not sure if i'm blind, stupid, or a little bit of both. but i've read the thread about tuning the nikki carb, and i cannot for the life of me find the idle mixture screw. front and center, driver's side of the carb and i dont see it :scratch: i found the idle set screw no problem!
there's this chrome cap/knob looking thing on the lower part of the carb, center. but it doesnt turn or seem to want to come off. seen here (if you can make anything of the pic)
Attachment 658523

any help would be greatly appreciated!
TIA

mixture adjustment screw is under the cap. :)

thanks! that cap just needed a little persuasion to come off.