A fuel valve comprising: first and second supply pipes (9 and 10) having first ends, respectively, suitable to be located in a tank in which liquid fuel and air coexist such that the liquid fuel and the air can flow through the respective supply pipes (9 and 10), whereby flow rates of the liquid fuel and air can be individually adjusted; a cap suitable to be fitted on the opening of the tank, wherein said cap defines a fuel mixing chamber, a flow rate adjusting member is received in the fuel mixing chamber, the flow rate adjusting member formed with recesses in a surface of the flow rate adjusting member, wherein the supply pipes (9 and 10) have second ends, respectively, kept in abutment with the surface of the flow rate adjusting member, wherein the recesses and the supply pipes (9 and 10) are configured such that the recesses can be moved relative to the respective second ends to predetermined positions where the recesses extend across and protrude from the respective second ends, characterised in that the liquid fuel and the air can flow through gaps defined between the respective supply pipes (9 and 10) and the corresponding recesses, the liquid fuel and the air are mixed together at a gap (g) that is defined between the inner wall of the fuel mixing chamber and the surface of the flow rate adjusting member, wherein the liquid fuel and the air that have flown into the respective recesses then flow into the gap (g) between the inner wall of the fuel mixing chamber and the surface of the flow rate adjusting member, before being discharged through a fuel discharge port, and the fuel valve has a discharge position where only air flows to discharge any liquid fuel remaining in fuel passages under pressure of the air. first and second supply pipes (9 and 10) having first ends, respectively, suitable to be located in a tank in which liquid fuel and air coexist such that the liquid fuel and the air can flow through the respective supply pipes (9 and 10), whereby flow rates of the liquid fuel and air can be individually adjusted; a cap suitable to be fitted on the opening of the tank, wherein said cap defines a fuel mixing chamber, a flow rate adjusting member is received in the fuel mixing chamber, the flow rate adjusting member formed with recesses in a surface of the flow rate adjusting member, wherein the supply pipes (9 and 10) have second ends, respectively, kept in abutment with the surface of the flow rate adjusting member, wherein the recesses and the supply pipes (9 and 10) are configured such that the recesses can be moved relative to the respective second ends to predetermined positions where the recesses extend across and protrude from the respective second ends, characterised in that the liquid fuel and the air can flow through gaps defined between the respective supply pipes (9 and 10) and the corresponding recesses, the liquid fuel and the air are mixed together at a gap (g) that is defined between the inner wall of the fuel mixing chamber and the surface of the flow rate adjusting member, wherein the liquid fuel and the air that have flown into the respective recesses then flow into the gap (g) between the inner wall of the fuel mixing chamber and the surface of the flow rate adjusting member, before being discharged through a fuel discharge port, and the fuel valve has a discharge position where only air flows to discharge any liquid fuel remaining in fuel passages under pressure of the air.