If the cotton is twisted to tight the
ejuice won't flow properly and will cause minor burning. Some flavors of
ejuice can make it hard to differentiate that minor burned taste from their flavor so it just tastes "strange." Thicker juices can cause this scenario as well.
Also I'd recommend gently torching the coils with a butane torch before you install them or gently dry burn the coil off and on for a couple seconds at a time before installing your wicking material. Heating the coil until it turns light red and then repeating the process forces the kanthal to anneal. Most builders don't torch their coils and this is why they notice a "warm up period" on their new builds. The heat annealing process also hardens the coil, which makes it much easier to install and replace wicking material on.