A special flush attachment is required for the 1971 model with the two piece foot. As far as I know, this flusher is no longer available. The simplest method for flushing would be to use a barrel, or a garbage can filled with water.
Its a 1971
The 1971 model, 18 hp Evinrude outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.
You can find an external wiring harness for a 1971 Evinrude 25 Hp outboard at different boating shops. You can also check with the manufacturer.
If you will go to Crowley Marine you can look up just about any old outboard motor. There is a diagram there for the 1971 25 hp Evinrude and if you will look there is a plate on the right side looking at the motor from the propeller end just below where the gearcase extension bolts on. It has several small holes in it and this is the water intake. On the Crowley gearcase drawing it is part #19.
A 1973, 50hp Evinrude outboard uses a 50:1 fuel to oil ratio.
The 1971 model, 125 hp Evinrude outboard, requires a 50:1 ratio, roughly one pint of 2 cycle oil, to six gallons of fuel.
You have a 1971 Us Made motor.
its a 1971
When they was new: 100:1 but i run my motor on 50:1 and it works well!
The correct plug gap for the 1971 model, 6hp Johnson outboard, is .030-.035 in. It requires a Champion J6J, or NGK B6S.
An 80 hp Mercury outboard, serial number 3055133, would be a 1971 year model.
The 1971 model, 50 hp Johnson outboard requires a 50:1 ratio, one pint of 2 cycle oil, to six gallons of fuel.