Carburetor and method of operating same

Claim 1

A carburetor for use in an internal combustion engine comprising: means defining an air-fuel mixture induction passage for supplying an air-fuel mixture to the engine, said air-fuel mixture induction passage including a venturi portion; a throttle valve in said air-fuel mixture induction passage; means defining a main fuel circuit; a main discharge nozzle of the main fuel circuit opening upstream of the throttle valve disposed within said air-fuel mixture induction passage of the carburetor; means defining a low-speed circuit; said main fuel circuit having a first passage providing in use communication for the main discharge nozzle with a fuel source; a progression chamber in the low-speed circuit, having a progression hole providing communication of the progression chamber with the air-fuel mixture induction passage, said progession hole being located above the edge of the throttle valve at the fully closed position thereof; said low-speed fuel circuit having a second passage providing communication for the progression chamber with said first passage; valve means for closing said second passage to block communication between said first passage and the progression chamber when actuated; a diaphragm-actuator for actuating said valve means upon having a venturi vacuum signal applied thereto corresponding to a high engine speed and load operation condition; and conduit means defining a passage for providing communication for said diaphragm-actuator with the venturi portion of said air-fuel mixture induction passage for applying to said diaphragm-actuator the venturi vacuum signal generated at the venturi portion, said passage being formed separate and independent from the main discharge nozzle and said first passage of said main fuel circuit and said second passage of said low-speed fuel circuit.