Johnson Evinrude Outboard Motors 1956-1970 1.5-40hp repair manual., Page 388Get this manual
MAINTENANCE
Standard OMC fuel tankDuring periods of storage the tank should be empty and the cap "cracked" open to allow the tank to "breathetr
the fuel tank containing fuel is to be stored for more than month, commercial additi ve such as Sta-Bil should be added to the fuelThis type of additive will maintain the fuel in "fresh" condition for up to full year3- Clean the carburetor fuel filters with benzol, see Chapter 4, Carburetor Repair Sectionfuel conditioner added to the fuel will keep it fresh for up to one full year