What happened to gasoline in the mid 1970s?

i think the reference is to unburned fuel in exhaust. The theory is that the stoichiometric ratio is never perfect and the mixture doesn't completely combust there by leaving unburned fuel in the exhaust stream. The "evaporative" emissions went through tubes to a charcoal canister somewhere on the vehicle, today with Fuel injection the whole system is sealed as far as evaporative emissions (fuel vapor). The cat converter is there to process unburned hydrocarbons and convert the gasses to inert gasses by way of catalyst. water is one of the by products you can see it coming out of the exhaust pipe.