I'm patiently awaiting an answer to this, too. I have it filled up all the way and I still get a burnt taste after a few puffs. It's the only one I tried out of the package - I guess I will try another one and see if it has the same taste.
On the CE2's (or flux) before using, even prior to using new ones (or if you get the burnt taste) I do the following:
1) Remove and rinse all plugs (Cap, inner ring, and ceramic cup ring - this one is a bit of a PITA to get out)
2) Rinse the cartomizer in hot water
3) Drop the cartomizer in boiling water (microwave water to boil), then drop cartomizer in for 5 minutes agitating occasionally
4) Rinse again
5) Shake excess water out, blow out excess water from both ends
6) Dry burn until you see all wraps of the coil burn red (typically three wraps), this may take a couple minutes
7) Fill w/ 1.5 mil on new/clean and 1 ml on refill (note: I do not replace the ring around the ceramic cup, I feel it reduces wicking on my higher VG juices).
8) Replace inner ring and cap (not cup ring)
9) Vape
This method works great on all CE2's I own from COV or Volcano (metal or clear). Dark and higher VG juices will require more often cleaning however I usually clean after 4 reloads and NEVER have a burnt taste with the above steps.
Hope this helps