Stale fuel

[chaz]

I wonder how fuel goes "stale" when I sold my trike it was over 6 years since it was last filled up, yes it took a lot of starting, the valve in the carb was stuck so no fuel getting in, flattened a new battery winding it over, but once it got some fuel through is started firing then running and then it was fine, I wonder if it's the engine that gets "stale" i.e. valves not seating maybe rings sticking plugs and points (not many of those about now) dirty, of cause there's the chance of water in the fuel also rust and dirt.
after all oil is 150 million years old?