A carburetor improves the starting performance of an engine. The carburetor includes a main body, a pump oil ball and a fuel-air mixing channel which extends through the main body. The pump oil ball is mounted to an air strangler spindle via a spiral groove. When the pump oil ball is pressed, the air strangler spindle is driven to rotate by the spiral groove and thus to control the air strangler spindle between the fully open state and the fully closed state. The carburetor dramatically improves the starting performance of the engine.