Morgy, with a new cart, pull off the black tip, then pull out the sealing ring that keeps it from leaking out. Just as you would to fill it, then, very gently, pull up a little on the bottom ring where the hole is for the wick. Just a little, not too much, that should help with the flow of juice from the wick. Do this on both sides. Some guys take it out completely and cut the opening in the rubber some to help the flow. I did that a few times, but found I didn't need to if I just lifted up a bit. At the factory they push those rings all the way down and they sometimes cut off the flow.
There is a nice video here.
510 CE2 Cartomizer XL
Try the steel revision 5 (fat wick) XL. If your liquid is still too thick, add some distilled water to thin. Not much, about .1ml per fill up. I use 50/50 and sometimes I add a bit to thin. I used to use vodka or everclear, but the alcohol can irritate your throat and cause a heartburn sensation. Once you figure it out, they are fantastic and really easy to clean.
Pull all the rubber out, soak in vodka for a couple of hours, shake out, (set out to dry a bit if you want), and dry burn until it glows nicely. I use them for about 10-12 refills before cleaning without any problem. I have used each one about 30 refills before I even consider changing them for new ones. I only had one rendered unusable due to me pulling the cup and everything else out when I was trying to clean it. I just stuffed it all back in and it worked fine! After 2 fills I just decided to swap it out for a new one. Other than that, they produce good vapor, last a long time, have great taste, and are really easy to use. I have never really had to "break it in". Use a drip tip if it seems too hot.
Keep at it and once you figure out the little idiosyncrasies, they are incredible. Note: the originals were kind of lousy, but the revision 5 is excellent with the fat wick.
Good luck, hope this helps.
Saludos