TOPIC:

I was curious if anyone had ever tried putting an O2 sensor with an air/fuel gauge on their bike. Most bikes don't have a fuel gauge and it looks like it might fit there (where the fuel gauge currently is). If not, it could be temporarily mounted just for tuning purposes, and then removed.

Seems to me that this would be more accurate than trying to judge plug color.

Keep in mind that a narrowband sensor will only tell you if it is richer or leaner than 14.7:1, and not by how much. To get reasonably accurate info you are going to have to go with a wideband senser, and that requires a controller and gets rather expensive (~$400).