One reason might be mismatched cylinder operation, but assuming you have GAMIs and got them sorted, an o2 sensor should work well, no?
I would imagine that as long as you are rich of peak EGT, there is in principle no surplus oxygen, so you would not be able to find e.g. best power setting, which is 50-100°F rich. Apart from that I have absolutely no knowledge of sensors or actual amounts of O2 that could tell whether it would be a practical way of detecting a useful economic mixture setting. I guess car engines all do that? but they need lead free fuel to work, right?
My guess is that temp sensors are cheaper than o2 sensors, but I may be mistaken
Lead?
Indeed, leaded fuel will kill an O2 sensor very quickly.
