I'm wondering, were you using a drip tip on the carto or maybe pushed the flexible tip in really far? Reason I'm asking is because the filler never touches the heating coil. The coil is completely covered by the silica tube press-fit over the top of it. So I'm thinking the only way filler could get burned is if it were pushed down super-hard so that somehow the heat could get through the silica tube and toast the filler.
Also, I've taken the filling out and put it back in on these carts and it's really tedious to do this. It's because of how hard it is to get that little blanket of filler around that tube. The best way I found is this:
Take a coffee straw or bar straw and push a nail, bamboo stick, or something into the end of it until it's just wide enough to slide over the silica tube, it just does fit perfectly. Then wind the filler blanket around the straw until it's tight enough to fit inside the cartomizer. Slide the coffee straw over the silica tube and then slide the wound blanket of filler down into the cartomizer. Then gently pull the straw out, leaving the wound blanket in place. Voila. Tedious, but doable.
'nuf said. LOL
Those plus a charger, an expensive loss.
