PURPOSE: To increase an amount of fuel to a main nozzle on the primary side during the starting and to improve startability, by a method wherein based on the number of revolutions of an engine during the starting and an engine running starting time after the starting, an electromagnetic mechanism to regulate a pressure in the suction pipe of the fuel increase system of a carburetor on the primary side is controlled.

CONSTITUTION: During the starting of an internal combustion engine, the number of revolutions of an engine is detected by a sensor 112 along with turning ON of an ignition switch 114, and an engine running starting time is decided by a timer 110. Based on outputs from the sensor 112 and the timer 110, a valve body 106 of an electromagnetic mechanism 102 is reciprocated by means of a control part 108. A power pressure passage 76 is opened and closed, and a pressure in a suction pipe exerted on a power pressure chamber 74 is regulated. Namely, through the energizing force of a power jet control spring 80, a valve rod 90 is depressed through a piston rod 82, and a power valve body 98 is separated away from a valve seat 100 to open a power fuel hole 88. This constitution causes increase of an amount of fuel to a main nozzle on the primary side.