Abstract: A liquid fuel supply system for an engine having a power demand adjuster, e.g. a manually operable control acting in conjunction with operational factors associated with the engine to determine fuel flow to the engine, in which apparatus is provided responsive to failure of part of the fuel system to cause an auxiliary to become effective to control fuel flow to the engine in accordance with the setting of the power demand adjuster, the arrangement being that for any setting of the power demand adjuster the fuel flow to the engine will not alter instantaneously when the auxiliary becomes effective to control fuel flow. It may be arranged that the relationship between fuel flow to the engine and the setting of the power demand adjuster may alter within a short period after the auxiliary has become effective.