1. There's a big possibility that the hole/slot that was put into the cartomizer is a bit to big. Which will lead to major flooding issues. Your not supposed to get any juice in your mouth at all. Especially when your taking a light hit. Also, if it's done correctly then the top of your atomizer should be dry most of the time.
2. Not at all. When you take a draw or a dry hit. That will draw the juice into the carto which eliminates the necessity to top if off. It's odd that your getting a burnt taste from what you described in your first post. But, if you are getting a burnt taste then immediately toss it. Since you are now inhaling smoke due to the filler and diaper (piece of cotton wrapped around your coil) is now burnt.
You should start off fresh with a new cartomizer. If you ever feel that it is tasting dry then you can do some dry hits and let it sit for a few minutes. So that the juice has a chance to be fed into the cartomizer and seep into the filler material.
3. All cartomizers are meant to be disposable. Some have better luck then others but, when you notice a hard draw and the flavor deteriorating. Then it's time to change to a new carto.
