Only real way to check air/fuel ratio is with a wideband exhaust oxygen sensor... the next best being a narrow band, and the next best (crude, but better than nothig) is the spark plug read.
Oh and if you look around for some carburetor tuning literature, you'll find graphs of air/fuel vs. economy, air/fuel vs. power, etc... maximum economy is achieved at about 15:1 air/fuel, but max power is at about 13:1, and idle mixture has to be a little rich for reasons already stated, and simply because your engine doesn't atomize fuel or make very good cylinder pressure at idle.
'86 Bronco fullsize, 460, E4OD
'85 Ranger, 340hp 289, T5
[ This Message was edited by: Motorhead on 5/9/06 12:16am ]