PURPOSE: To reduce an amount of smoke produced when a low-speed operation condition is changed over to a rapid acceleration condition, by reliably preventing starting fuel increase in a high-load range from occurring in a larger number-of-revolution range than an idling number-of-revolution range.

CONSTITUTION: A control sleeve 10 is linked with one end of a start lever 12. This start lever 12 and a tension lever 19 are supported on the same fulcrum 13, and, between those levers 12 and 19, there is mounted a start spring 21 intended for urging the start lever 12 in a direction to cause an increase in fuel. At a starting time when no thrust is produced from a mechanical governor 14, starting increase in fuel is effected by the urging force of the start spring 21. A piston mechanism 24 operates with a rise in the fuel pressure inside a pump chamber 5 and limits the rockable range of the start lever 12 to a suitable range via a stop lever 22.