You should never change fuel ratio based on year. And a blanket 50:1 is very dangerous. My info from a 50+ year Evinrude dealer is 50:1 back to 1960 on larger omc motors.This is based on engine design not the year made.You need a full ball/ roller bearing powerehead.Present day gas has no affect on fuel mix ratios the improved oils do help some.The oil is the life blood for a motor we shouldn`t mess with ratios unless supported by qualified expierence. I accidently went to 100:1 on my almost new 88 50 Evimrude it did fine for over half the season with my old timer cruising at 3/4 throttle etc. until my son spent the weekend skiing with his buddies.It lasted one afternoon.$800 later I keep the bill next to the oil.There are some motors that some folks actually reccomend going slightly on the rich side.Keep in mind too that on the old motors with adjustable highspeed needle valves if you adjusted too lean you could ruin a motor.Even a full bearing powerhead running on 24:1.I`m pretty consertive and even with that dealers info I would probably run at 32:1. if I was going to mess with my ratio.