I don't go past 3.8v on a 2.0 Ω.  After that. it starts getting pretty hot.
On the flooded cartomizer  I have blown into the connector end while holding a parer towel on the other end without removing it from the tank (remove the drip tip first).  Then make a tip on the end of the towel, and insert it into the end where the drip tip goes.  Replace the drip tip, relate it on the battery, and fire it a couple of times.  You should hear a popping noise.  Take a puff and see if that fixes it.  You shouldn't draw too hard on a cartomizer.