Abstract: An actuating mechanism for varying the Venturi gap of a jet dyeing machine allows adjustment of the gap between a zero spacing (for easy centering) and a self-cleaning, fully open position, adjustment being provided without interrupting production. As is conventional, a textile material passing pipe is reciprocal within an outlet pipe, with an end of the textile material passing pipe forming a Venturi with a circumferential lip formed on the interior of the outlet pipe. A cam and follower mechanism is mounted exteriorly of the textile material-passing pipe between it and the outlet pipe, with a cam shaft extending through the outlet pipe wall to an exterior position. Power means, which may be responsive to sensors for sensing fabric flow and liquid flow, effect rotation of the cam shaft to effect reciprocation of the textile material-passing pipe, and thus adjustment of the Venturi gap.