1990 Johnson Evinrude "ES" 9.9 thru 30 Service Manual, P/N 507871, Page 60Get this manual
Description of Fuel System 1The fuel pump is of the diaphragm-displacement type, and is operated by changes in crankcase pressureAlternately, suction and pressure in the crankcase are transmitted to the pump diaphragm
The carburetor meters and distributes the fuel consumedThey control engine speed and power output by varying the intake charge densityTo react correctly to wide range of operating conditions, the carburetors have multiple fuel mixing circuits