I recall my dad’s car got tested. CO was practically nothing.
I guess he had a catalytic converter.
My understanding was that in a poorly ventilated garage, CO would have been produced.
High school chemistry C8H18 + 17O2 = 8CO2 + 9H2O.
In theory, theory and practice are the same. In practice they are not.
I see your point, so I guess that 100% proper combustion isn’t possible for gasoline, at least in an internal combustion engine. Maybe cleaner in open-air burning, but I have no clue.