1997 Johnson Evinrude "EU" 40 thru 55 2-Cylinder Service Manual, P/N 507265, Page 66Get 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
2The carburetors meter and distribute 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 circuits3The unit is combination mechanical fuel and oil pump, powered by crankcase pressure and vacuum pulses, which responds to various engine power settings by injecting the proper amount of oil into the fuel system