A mixer for exhaust fume recirculation burners, defining a first inlet section for a flow of comburent air, a second inlet section for a flow of recirculation fumes, a mixing chamber for said air and recirculation fumes and an outlet section for a mixture of said air and recirculation fumes, said mixer comprising: - a first valve device interposed between said first inlet section and the mixing chamber for controlling a flow rate of said flow of comburent air; - a second valve device interposed between said second inlet section and the mixing chamber for controlling a flow rate of said flow of recirculation fumes; - an activation device active on said first and second valve device (20, 30) for simultaneously activating said first and second valve devices (20, 30); - an adjustment member interposed between the activation device and at least a respective one of said valve devices (20, 30) for defining a movement of said respective valve device (30, 20) following an activation of said activation device, and in that said adjustment member can be configured according to a plurality of different configurations so that a same actuation of the activation device corresponds to different movements of the respective valve device (30, 20), said adjustment member being associated with an adjustment means configured to set said configurations of the adjustment member; said adjustment member comprises a cam mechanism with a variable geometry, said adjustment means being active on said cam mechanism for varying the geometry of said cam mechanism; characterised in that said activation device comprises an activation shaft and wherein said cam mechanism having a variable geometry comprises: - a curved guide rotationally solidly constrained to said activation shaft; - a cam follower engaged on said guide and connected to said respective valve device so that a rotation of the activation shaft determines a corresponding movement of said respective valve device. - a first valve device interposed between said first inlet section and the mixing chamber for controlling a flow rate of said flow of comburent air; - a second valve device interposed between said second inlet section and the mixing chamber for controlling a flow rate of said flow of recirculation fumes; - an activation device active on said first and second valve device (20, 30) for simultaneously activating said first and second valve devices (20, 30); - an adjustment member interposed between the activation device and at least a respective one of said valve devices (20, 30) for defining a movement of said respective valve device (30, 20) following an activation of said activation device, and in that said adjustment member can be configured according to a plurality of different configurations so that a same actuation of the activation device corresponds to different movements of the respective valve device (30, 20), said adjustment member being associated with an adjustment means configured to set said configurations of the adjustment member; said adjustment member comprises a cam mechanism with a variable geometry, said adjustment means being active on said cam mechanism for varying the geometry of said cam mechanism; - a curved guide rotationally solidly constrained to said activation shaft; - a cam follower engaged on said guide and connected to said respective valve device so that a rotation of the activation shaft determines a corresponding movement of said respective valve device.