I dunno if you caught what I was saying in the previous post, but if the core of your wick is black, that means you're not giving the coils enough heat, in some way shape or form. The blackness (and someone else posted this or told me this) is caused from the juice not being completely vaporized effectively. Like I was saying, it happened to me before, but now that I have switched to my mechanical mod and using the correct ohm coils on it, not a single wick for me has turned black. Another thing of note, with my iStick TC40w, Ni200 coils were turning black and I thought the coil was burning up, but found out after a closer inspection that the coils were not heating up quickly enough. After speculation of this, I ran an Ni200 coil for far longer than I normally would have to see what would happen and bam, the black gunk on the coils began burning off giving an awful flavor. Essentially, the gist of this all is, the coils need to be the correct ohms for the correct mods, or juice will be ineffectively vaporized and begin to turn black and get gunked on coils and wicking.