Heres another usefull page, to tune carb after removing airbox, , My ZL900 ws overich when i got it, [black sooty exhausts,] i removed air filtre , and a massive improvement , took carbs off to set float level, and checked the pilot screws, 4 turns out, [ that richens these carbs,] set them back to 2&1/8. and problem solved,,, ..read this page,,
http://bikeadvice.in/fit-kn-filter-rejet-carburetor/