G.R. Patterson III wrote :

I've been running my 1940 Ford on the same tank for three years now
(obviously I
don't take it anywhere -- just run the engine a while).

You've been fortunate to get a tank of extremely stable gasoline.
Over the last few decades, I've stored a number of motorcycles in my
garage for varying periods. I found that autogas would start to smell
funny after a year. After 2 years, it transformed itself into
something that looked and smelled exactly like turpentine. Needless to
say, by the time the fuel got to that point, the carburetor jets were
hopelessly clogged with a nasty gummy substance.

If you use a gasoline stabilizer like Sta-bil, auto gas can last
quite a bit longer. Fuel makers recognize that planes may go awhile
on the same tank of gas, so they formulate avgas accordingly. Last
time I checked, Chevron and BP both said their avgas would be fine
after a year.

John Galban=====N4BQ (PA28-180)