Stock coil, starts tasting burnt, time for a new coil. Stock coil cleaned, with new cotton flavor wick, starts tasting burnt or wonky, time for a new coil. Recoiled with cotton wick no flavor wick, tastes great for a week, after maybe two, tastes fine but maybe not great and the draw gets maybe a little tight. Do I need a fresh coil? Maybe let it go for a couple more days. Gee, this juice isn't quite as good as I remember. Heck, I'll put in a fresh coil. Couldn't hurt. Man, this old wick looks like a slimy black worm.Voila! This juice is a great as I thought it was! Lesson learned? Cotton wicks don't tell you when you need a new one. A degradation in flavor is the only clue and it's so slow that it just kind of creeps up on you. When in doubt, recoil/wick.