1. Use thin juices. What juice are you using. I recommend PG with 20% or less VG for stuffing cartos and 20-30% for reservoir cartos, at least if the cartos are new to you. If juice is too thick, it will not wick fast enough to keep the coil area damp and you get burnt taste or singeing.
2. If you have never used cartos, I recommend learning on Boge standard resistance - I will attach how I fill those. LR are the same but hotter and less forgiving - they will singe easier if you don't fill them properly and keep them damp
3. CE2 suck - you have to screw with them, they fall apart and crack, the wicks can be trapped under the inner seal and not wick right. If you want to try clear ones, maybe try the Deluxe Fluxomizers at Gotvapes - those are a prerelease or initial release version of CE3 Smokymizers which are supposed to have less problems.
below - how I fill stuffing cartos (I use standard resistance Boge)
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How I fill a cartomizer (Vapor4Life for KR8 or Boge 510 for 510 which are all soft-cap w/ no inner seals and defined central air channel)
I use thin (20% or less VG) liquid or Vapor4Life WOW liquids, preferably clear liquids w/ no sediment
Filling a blank carto - I pop off the soft cap (unbent paperclip carefully in the mouth hole, not catching any wires or stuffing!). I hold some tissue against the threaded end hole. I tilt the carto and slowly drip 18 drops (per ml of carto capacity and these are 1ml cartos) onto the inner wall of the carto so it slides down into the stuffing while I rotate the carto. Then I wait 15 seconds or so then I drip however many more drops the stuffing wants to soak up. Then I do clean-up. If it is leaking, I clean that up. Then I tilt the open end down into the tissue and puff hard a few times into the threaded end to clear any juice out of the central air channel (I want to see light through there). If it looks too wet above the stuffing, I gently touch a bit of tissue to the stuffing (otherwise that liquid will be gurgling or spitting in my mouth). Then since this was a fresh fill of a blank, I now let it settle. I lay the carto on different sides for 15-20 minutes. Then it should be ready to vape. If you use thicker juices than me, then you may need to let it settle longer.
As I am
vaping - if the vapor gets a bit light or a bit dry or tastes bit off or the carto is getting unusually warm, I will take the carto off the battery, open it, add 6-8 drops or whatever it seems to want (I will either hold a bit of tissue against the threaded end hole just in case, or skimp on how many drops I add to make sure I avoid drips if I have no tissue). I check to make sure the threaded end is dry, give it a couple of puffs into the threaded end to make sure the air channel is clear, and continue to vape.
Note - it is easy for me to "open" my main cartos for adding juice because I replace the white end cap with a plastic or delrin drip tip (I get them at LiteCigUSA.net). So I can easily pull that out with my fingers when I add juice and it keeps my lips cool if the carto is hot.