PURPOSE: To enhance the exhaust performance at idle of an engine having an electronically controlled carburetor.

CONSTITUTION: A detector 10 for the opening of a throttle valve 11 and an engine speed detector 12 are operated in conjunction with a throw type fuel control 14 via a control means 8. When the opening detected by the opening detector 10 is lower than set opening and the engine speed detector 12 does not detect hunting, the throw type fuel control 14 reduces the amount of fuel supplied from a throw type passage 5. Therefore, since the amount of fuel supplied from the throw type passage 5 can be controlled by the feedback of information about the opening of the throttle valve 11 and the engine speed, the amount of fuel supply can be reduced to a necessary amount without increasing engine speed at idle operation, resulting in enhanced exhaust performance and combustion performance.