Hello eveyone, long time no post, but Erika I ran into the same problem you are having sometime ago and in my IMHO it's not the way you are filling them it's the cartos with brass threads are just absoluely terrible, burnt taste no matter what you do but as pointed out to you earlier if you get the silver threaded Boge cartos that will rarely ever happen. Just very hard to make sure you get the right ones because soooooo many e cig vendors have very little if any information about their products. Hope this helps and good luck