I have the best results when I don't overfill those with juice, especially if they come a bit overstuffed (with filler) to begin with. Decreases the airflow through the carto, in my experience. I refill early and I refill often. And I always inspect the insides of the carto before I vape it to make sure the filler is evenly saturated and that the airflow tube is centered. If not, I run a thick sewing needle through it to recenter it.
Yep I definitely think this was my issue. I haven't gone back to try to revive the ones I put in the box as dead yet but I'm going to. I've been going thru these like crazy and really can't afford to use two of them every day. I also now blow them out before I fill them. I did notice that although my menthol juice is quite clear when I blew out the carto dark brown almost black juice came out so I know I overfilled and then the extra juice just burned and was NASTY. So I cut back from putting like 15-20 drops in every 3 hours to just putting in about 10-12 every hour. Kind of like getting my ciggy ready to go when I smoked, lol!
In summary - do NOT overfill these! It is the bane of their existence!
I wasn't going to order anymore but now I'm going to... just got some peach cobbler from TV and I CAN'T WAIT!