Yes, petrol does go stale.
Whether you are storing fuel in a gerry can or just not using a recreational vehicle regularly enough, the fuel will start going off.
In as little as 3 weeks, fresh petrol can start changing its chemistry due to oxidation, often accelerated by the presence of dissolved metals in the fuel.
After 5 weeks’ fuel can be 5% heavier and 5% richer air fuel ratio.
This process presents itself in the formation of gums and varnishes which clog up the fuel delivery jets especially in carburetors, making starting difficult, as well as peroxides which can eat away at metals and rubbers in the fuel system.
Incombustible deposits foul up the combustion chamber while the oxidized fuel (often darker in colour) becomes denser making the air fuel mixture too rich leading to running problems.
By using a Fuel Stabiliser in the fuel when an engine stands over prolonged periods, prevents this oxidation as well as corrosion, allowing better combustion, performance and less maintenance.
Also works in diesel.