I just recently have poured over parts for ALL the years of 18’s looking for pistons for my rebuild. Frank is right there isn’t much difference in them at all. If I had a 1950’s era 18 I would surely run a leaner mix than 24:1. The oils we have available today are MUCH better. I have a 1968 18 that I run basically a 50:1 mix and I throw in 1 more oz for a 6 gallon tank, instead of 16oz of oil per 6 gallons I mix 17. The motor doesn’t complain and it runs like a cat kicked in the butt and doesn’t foul plugs. My best friend has a 1965 18 that I maintain and he too runs the mix I do and doesn’t have any trouble with his either. We both run the Johnson Evinrude TCW3 2 stroke oil that they sell at Walmart by the gallon.
