I need the oil mix rate for 115hp evinrude 1980 motor.

Ask a Marina.

50 to 1 87 octane gasoline to TCW3 certified oil. Higher octanes will just result in a less complete burn.

1/3 cup oil per gallon of gas, one pint per six gallons, is 48:1, so u can round to the nearest ounce with no worries.

recent acquisition? if u do not know the age of the water pump impeller or if its more than two years, this would be a good time to change it - downside of pump failure is catastrophic.

use only Champion QL77JC4 spark plugs at .030 - not just a personal brand preference - that engine really will do better with champs.

prop it to where it will turn 5500-6000 (closer to 6000) at WOT, any less is lugging, any more is overrev. select a prop for WOT RPM is & u will be good across the whole range of throttle settings.

That is one of the best motors ever made, just needs a little preventive maintenance, it will still be running after we're long gone.

50:1

That is one pint of oil for every six gallons.

Of course on your boat you probably have a built in gas tank.
So what l do for my clients is laminated a 50:1 chart, (built in Excel) that they can stick in the glove box as a cheat sheet.

Have a great summer.