[dragbaron]

Was pretty hard on the Shadow the past two days with the last run being a long 5th gear pull to unknown speeds(crappy 125 speedo!). After that run it started to miss at idle and steady cruise(was fine when accelerating). Got home and found the miss on the #3 cylinder. Pulled the plug and the porcelain peice had come loose and would slide up and down the center electrode. It is light tan in color with some glaze to it(from the high speed runs I guess). I had another Autolite #63, so it's running back to normal. Was this a problem with the plug, or did something in my setup cause this.

 

[NAJ]

It sounds as if you just have a defective plug, keep an ear open for detonation.
Check this link for pics of plug condition.(googled spark plug condition)
Spark Plug Analysis