My understanding is thus: Any vehicle with a 3-way catalytic converter really requires TWO O2 sensors so that the exhaust mixture can be precisely controlled and monitored. They typically need to run a bit rich to give the cat something to burn and prevent nitric oxdide, something a 2-way or 1-way cat can't do. I believe the cats in the C14 are the same in all markets and are not 3-way (please, someone correct this if it is wrong).
Every model of the Concours 1400 COULD have a SINGLE O2 sensor, it depends on the market. In the USA/CA market (NA), it was omitted. However, when they started winding down the C14 in the rest of the world, Kawasaki finally put the O2 sensor in the last few years of the C14 in the NA market (I think 2017/18).
An O2 sensor enables the ECU to more precisely measure the mixture in the C14. I suspect the only reason Kawasaki didn't just use an O2 sensor for all markets (presumably to meet stricter pollution controls, like our cars here have been for a loooong time) was cost. But it really isn't THAT expensive for a system already designed for it (like the C14 was), it is just a sensor and cable.... $50? $75? On a $16K bike, that is nothing! I have wondered about that for ages, but never saw an answer, and never asked... we might never know.
[The ultimate would be to also include a mass air flow sensor (like cars forever, now) so the bike would not have to rely on the obsolete "MAP" sensor to "guess" how much air based on computed tables.... but I guess that is a different discussion.]
As to why a tuner might disable the O2 sensor- it is primarily because that added input interferes with their hard-earned research on the models that don't have it. The O2 C14 will use the sensor to help map fuel mix at lower throttle positions, possibly "interfering" with the tuner's table. Its input is primarily emissions-centered and doesn't help with performance objectives. But I doubt a
stock C14 with or without O2 sensor makes any noticeable difference to the driver.
Great topic, I am anxious to learn more!
