Re: 1964 Evinrude Fastwin 18 hp
Well it's really a matter of the internal components of the engine, not so much what the factory said. The factory is/was/can be wrong at times. If the motor uses needle bearings, then a leaner mix can be run (i.e. 50:1 vs. 24:1). However, I always err on the side of caution with these old motors and use extra oil (too many stories of great old motors overheating and seizing up because "the previous owner said I could run *insert improper fuel oil mix here*.") A fellow member in the forums made a great analogy that oil is to these old motors as water is to an athlete. While you can certainly have too much, generally speaking, they both like to be well lubed. I run 24:1 in my '66 20 hp without issue and virtually no smoke while out on the water. To me it's cheap insurance, even if it isn't entirely necessary. My motor my die, but it won't be for lack of lubrication. Plus, I can always cut the fuel I run with straight gas in a pinch and still have plenty of oil in the mix. Kind of nice when you run out of oil, or you're at a gas station that doesn't sell any and you don't have to time to track some down.