Yes - if you singe cartomizers they will taste burnt and bitter. If you don't fill them TO STATED CAPACITY with appropriate juice and then let them settle a bit you will singe them. If you run them nearly dry, you will singe them. If you singed them, a refill will not fix that.
I don't refill cartomizers. I keep them damp and never let them get low on juice. I can get 7-10 days use or about 20ml of thin clear juice usage out of each cartomizer.
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How I fill V4L/Volt/Bloog KR8 cartos and Boge 510 cartos (1ml capacity)
With the carto off the battery... Pop out the soft cap with an unbent paperclip in the mouth hole, very careful not to catch stuffing or the wire loop.
Shake and open the eliquid
Fill
Hold a bit of tissue on the threaded end hole (or use the carto condom spike to block the hole),tilt the carto, and add 18 drops per ml of capacity into the stuffing (Boges and most KR8 cartos are about 1ml). You may need to wait a bit for the first few to soak in, then continue. After getting the 18 in, wait 15 seconds or so then see how many more drops the carto stuffing will soak in easily.
Cleanup
Clean up the threaded end, tilt open end down into tissue, puff into threaded end to clear air channel (Boges and the KR8 cartos I use have a defined center air channel and I want to see light through that) While the carto is still open end down, touch a soft bunch of tissue to the top of the stuffing to get the loose juice - this will help prevent leaks.
Settle (first fill only)
Cap and let it settle - I lay it on different sides and on the ends for 15-20 minutes to make sure every bit of stuffing gets damp so I won't singe the carto. if you use thicker juice than me (I use 20% Vg or less) then you may need to wait much longer.
While
vaping
While
vaping, if the vapor gets a bit light or a bit dry or the carto is getting hotter than normal, I take the carto off the battery and add eliquid. Also, I use such light sediment-free juices, I can look at the stuffing and see if it needs juice because the stuffing goes back to near-white.
I often use a plastic or delrin drip tip as a mouthpiece on Boge and KR8 cartos (not to drip into since the juice would head for the central air channel). Easy to pop out to add juice. I use thin clear juices, PG w/ 20% or less VG and I avoid all dark. opaque or cloudy juices that drop flavoring sediment in the stuffing (degrades a carto real fast)
