A couple of days ago, someone was having flavor issues that we never got sorted out.
Lack of flavor is usually caused by two things.
You need to take long, slow drags. Short hard drags will not work well on the Zens because you really need time for the airflow to work as designed. Long hard draws will result in little or no flavor.
Also, flooding will result in poor flavor. You need to vape at 3 o'clock until the wick is broken in. After that, vape at 4 or 5 o'clock. Vaping at too high an angle after the break in period will result in flooding. Over wicking gives poor flavor.
You might also want to put a small pinch in the top of the wick which will cause the ejuice to be in contact with the coils for a longer period which will result in better vaporizing of the juice and less condensation in the top cap which can also cause flooding.
Continuing to draw for a second or two after letting go of the switch will help prevent condensation forming in the top cap, which in turn will cause darkening of your juice in the tank as it runs back down. This is just carmelization of the sugars in your ejuice and is not harmful and generally not noticeable in the taste. However, it may not be esthetically pleasing to the eye.......LOL