I fly a Zenair Zenith 200 with a l986 13B.  I have installed a Cyberdyne Instruments bar graph air/fuel gauge (P/N 7009). The O2 sensor is located ~31 inches from the exhaust ports. The O2 sensor is not a Cyberdyne Instruments part. It is an aftermarket universal single wire sensor. The readings of the air/fuel gauge are baffling me. At idle of 1100  rpm and MP of 14.1-14.2 inches/mercury, the air/fuel gauge shows a rich condition of ~12.7:1. That is where the engine runs best at idle. At full power static of 5200-5250 rpm and MP of ambient (~30 inches/mercury), the air/fuel gauge reads rich ~13.2:1. However, when I retard the throttle to 3000-3500  rpm, at a MP of 17.0-17.1 inches/mercury, then the air/fuel gauge reads lean at ~16.0:1. The engine runs quite evenly at all power settings but I wonder if the variations in fuel mixture are normal and safe?
Yvon.