A self-regulating fuel vaporiser comprising a fuel-air conduit adapted for series connection between a carburetor and an inlet manifold of a spark ignition engine, and including a heat exchanger having a plurality of mutually parallel, thermally conductive vaporiser tubes and at least one thermally insulated by-pass tube, all transversely intersecting a region of said fuel-air conduit, a first exhaust conduit arranged in series flow connection with one end of each of said vaporiser tubes and said by-pass tube, a second exhaust conduit arranged in series flow connection with the other end of each of said vaporiser tubes and said by-pass tube, said first and second exhaust conduits being adapted for connection between two consecutive portions of an exhaust pipe of said engine, and a plurality of mutually parallel, planar vaporising fins disposed within said region of said fuel-air conduit in a direction normal to said vaporiser tubes and said by-pass tube, each fin occupying the full width of the surrounding conduit and each being intersected by every one of said vaporiser tubes and said by-pass tube, and being thermally coupled with every one of said vaporiser tubes.