1988 Johnson Evinrude "CC" 9.9 thru 30 Service Manual, P/N 507660, Page 81Get this manual
Description of Fuel System
1The fuel pump is of the diaphragm-displacement type, and is operated by changes in crankcase pressure Alternately, suction and pressure in the crankcase are transmitted to the pump diaphragm
2The carburetor(s) meter and distribute the fuel consumed They control engine speed and power output by varying the intake charge densityTo react correctly to wide range of operating condition, the carburetors have multiple fuel mixing circuits