PURPOSE: To contrive not to allow an engine to stop even when an vehicle is started immediately after the starting of the engine at low temperatures, by permitting a thick mixed gas to be supplied from a slow system port when a starter is in use.

CONSTITUTION: A plunger type starting valve 39 is formed with a large diameter guide 41 that is slidably guided within a guide bore 42 formed in a carburetor body 1. A second slow air bleed path 2 has an upstream side path 29a and a downstream side path 29b that are in communication via the guide bore 42. When the plunger type starting valve 39 is pulled out, the communication of the upstream side path 29a with the downstream side path 29b can be cut, and a second slow air bleed path 27 is closed.