Outboard boat motors with two cycles manufactured by Johnson and Evinrude after 1964 require a 2 percent fuel to oil mixture. Use 1 cup of outboard motor oil for every 3 gallons of gasoline.
The oil needs to be manually added to the gas tank unless the engine has an automatic oiling system. If the motor was manufactured before 1964, a whole pint of oil should be added to three gallons of gasoline. The addition of oil to the gasoline causes the gasoline to become thick and clog the fuel lines. Only mix the amount of fuel needed for the day. If there is some left in the tank, do not let it sit for long without cleaning the system.