"I agree the original mixing r
"I agree the original mixing ratio was 20:1. However, lubricants have advanced dramatically and I have been running my vintage outboards for over 25 years now without a single failure. My everyday trolling motor is a 1965 Evinrude 6hp and I have run fully synthetic 100:1 Amsoil mixed at 64:1 or 2oz per gallon.......or to be more precise, 12oz per 6 gallon. Be sure to use non-oxy fuel as ethanol will destroy rubber composition parts such as crankshaft seals, gaskets, hoses and diaphrams. I enjoy the 50's and 60's outboards because of their simplicity and reliability. The original recomended mixtures caused heavy emissions into the water, created disgusting smoke and carbon deposits inside combustion chamber and exhaust discharge surfaces. The motors of this era were engineered brilliantly but the lubricants were very poor. I have had water pumps fail over the years, causing only minimal cyl/piston scoring while using Amsoil at this ratio. The ability of this synthetic formula to protect surfaces at extreme temperatures is far superior to petroleum or petrol/syn blends.
Note....you might want to replace the head gasket then inspect and decarbonise the combustion chamber. See if any damage was done by the overheating. Good luck, Tim"