Well on my friends car it always idled rich , it made no difference where you adjusted the mixture screws so we used a slightly larger bleed , it clean up immediatly .
we have tuned the jetting as well if you have to increase jetting your bleed may be too small creating vacuum inside the air bleed tube , possibly a slightly smaller bleed will clean it up with out or in conjunction with jet changes .
Think of it this way , you are drawing fuel out the bottom of a tube through a small orifice [mixture screw or jet], the tube is being fed from the side 2/3 of the way down , at the top there is also a small orifice restricting air flow into the tube . The smaller the restriction at the top the more fuel is pulled in through the jet or idle mix screw , if you open the top orifice it will draw in less fuel through the same hole as some of the vacuum is lost through the top .
