Weft feeder with adjustable-diameter drum for weaving looms, comprising an electromagnet unit controlling the weft thread release equipped with a quick-release device to adjust and fix its working position

Weft feeder for weaving looms with thread coil separation, comprising a winding group (W) to wind a weft thread on a drum (D) of the weft feeder, and an electromagnet unit (E) to control the movement of a stop pin (P) which prevents the weft thread from being released from said drum (D), wherein said electromagnet unit (E) is movable in a radial direction with respect to an axis of the weft feeder drum (D), along guide means (1, 2) provided in the base body (C) of said weft feeder and in said electromagnet unit (E), respectively, and wherein said guide means (1, 2) comprises a pair of fixed guides (1) and a pair of mobile guides (2), both parallel to said radial direction and mutually coupled, at least one of said fixed guides (1) and a mobile guide (2) coupled therewith having flat contact surfaces (1a, 2a) inclined with respect to the weft feeder axis, characterized in that a single locking/unlocking means (3, 4) is also included, having an axis parallel to the drum (D) axis, for stably fixing said electromagnet unit (E) in a predefined position along said guide means (1, 2), so that upon tightening said single locking/unlocking means (3, 4) said guide means (1, 2) automatically cause centering of the electromagnet unit (E) with respect to the weft feeder axis, and prevent its rotation about the axis of said locking/unlocking means (3, 4), wherein said single locking/unlocking means (3, 4) includes a pawl (3) housed in an undercut recess provided between said pair of fixed guides (1) or in the weft feeder base body (C), and a tierod (4) connected to said pawl (3).