the O2 sensor creates a closed loop. Why would the bike move in and out of closed loop? Does the O2 sensor on the bikes in your country have a heater on them?I don't have such issues. however, I would recommend taking the O2 sensor out (you can get for cheap the O2 sensor eliminator). the one from Vulcan S will fit: Oxygen Sensor Eliminator kit
with O2 sensor present, the bike moves too much between open and closed loop, and the transition is not smooth.
also installing booster plug will no doubt help.