Abstract: A fuel system adjustment tool includes an elongated shaft and a rotatable rod disposed within the shaft. At one end of the rod is a drive that operably fits to an adjustment point on a carburetor. At the other end is a rotatable knob that produces a tactile engagement or clicking sensation at selected degrees of rotation, preferably every 180 degrees of rotation. The engagement is produced by a collar having a notch therein on the end of the shaft, and spring loaded balls in recesses on the interior of the knob. As the knob is rotated, one of the balls falls into the notch at the selected degree of rotation, but is releasable from the notch upon further rotation.