I posted a thread about this a couple days ago.. but I recently got a 5pack of XL Clearo ce2's as well... On CE2 #4, I finally figured out how to get these things to wick correctly (without a tank mod)
I take them out of the clearo tube, I untwist the ends of the wicks (so they are strands) I then burn each side of the wick closely up to the ceramic cup with a butane torch lighter ( don't worry, they won't burn ).. then I screw the clearo guts onto a battery and proceed to dry burn it for a good couple of minutes (before ANY juice is added) I keep my eye on the coil, making sure that the coil is heating evenly and properly... then I slip them back into the tube, and add my juice.
Once juice is added, the best way I've found to tell if a ce2 is 'working' is to take your drip tip off, and fire it while looking at the coil. If it's wicking properly, the coil *should not* get red, the wick should be replacing the e-juice faster than the coil can vaporize it, thus keeping the coil cooler than red-hot. I use this test to see the highest voltage my current ce2 can 'handle' (vape without the coil turning red.. i've found once the coil gets red is when you get the nasty taste/burnt feeling).
All the CE2s I opened BEFORE I found these methods... I can't even use them on a standard 3.7v device without the coil becoming glowing-red in a matter of seconds.. the ones I did the slight modifications on can go on my VV box up to 5v without the coil getting red (It does get red at 5v.. but only after holding the fire button down for much longer than any normal drag)