Also one of the biggest problem with high performance outboards is a low grade of gasoline. What burns fine in a car can destroy an outboard motor. I have an Evinrude 115 in my shop right now with 3 burnt piston, looks like somebody took a hammer and chissel to the top of the piston, but, in this instance it appears to be old gas in the tank that has lost its octane.
I’m happy that my old ‘63 Elgin 45 was designed to run on 87 octane. A year or two later they required premium (increased compression and timing advance?).
Although I do have some fuel left over in the tank each spring, it has plenty of stabilizer in it and I mix it with new fuel.
Since ethanol blend fuel might be expected to lose more octane than straight gasoline, I might start buying premium for any storage need. I know the volatile stuff in the blend fuels disappears right off the bat.
I do worry somewhat about the diaphragms in those old Walbro carbs.