What is the fuel mix for a new 1982 4.5 hp Johnson outboard?

Mixture should be 2% or 50:1

That would be a little over 2.5 ounces per gallon or

Roughly 8 oz (1/2 of a 1 pt bottle) to a three gallon container.

Put the oil in your container first and let the gas mix it up with pressure from the nozzle. When container is about 1/3 full shake it up to get the oil off the bottom of the gas can. Continue filling until you get to the desired amount.