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 for simultaneously activating said first and second valve devices ; - an adjustment member interposed between the activation device and at least a respective one of said valve devices for defining a movement of said respective valve device 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 , 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 for simultaneously activating said first and second valve devices ; - an adjustment member interposed between the activation device and at least a respective one of said valve devices for defining a movement of said respective valve device 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 , 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 . <EOS>