O2 Sensor on a Carb Engine Question

I use an AEM on my 408. If the O2 fails, it seems to default to stoich and freeze there. As others have pointed out, it reads unburnt O2, so any misfire, or a fouled plug, can cause false lean readings. This is why the bolt on TBI systems get a false "Bad" diagnosis. They run in a default open loop when cold (rich) and if you start it and move it 10 times, and shut it off cold (think of moving it around a garage in the winter) it soots the plugs, runs worst, soots the plugs more, and when it finally kicks to close loop when warm, it reads the unburnt fuel from the fouled plugs, and pours even more coal to it.