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.
Four cycle, Fog the motor as below. Do not put any oil in the gasoline. Do use stabilizer. Change the motor oil, replace with Evinrude or Johnson, Mercury/Quicksilver or Yamaha or Tohatsu/Nissan...
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...
The 25 hp Evinrude outboard has been designed to run a 50:1 ratio, for earlier models, and 100:1 for late model engines. Pre 1965 models run a 24:1 ratio.
There are 2 models from '63 at 28hp - models 28302 and 28303. Model 28302 is a standard length shaft for 15" transoms and 303 is for 5" longer for 20" transoms.
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