Originally Posted by Frank Reiner

T7:

Whether the Holley carb is a 2-barrel or a 4-barrel, there are idle mixture screws exposed laterally a bit below the mid-line of the float bowl. There is a screw on each side. The screw heads are quite small, about 3/16" in diameter. With a small screwdriver, unscrew each mixture screw in turn about three turns, then back in the same amount, plus 1 additional turn, then back to the original point. This "exercising" of the mixture screws may release some of any built up fuel residue, and gum, allowing fuel to flow again in the idle circuits.