I have never had success with cartomizers and im thinking they may have dried out or something becouse of not much vapor. At this point i am vaping only at 7v+ and as Emonty said carts are mainly for 3.7v which i feel as well. Since i started vaping, Ive used nothing but 901's, HV, LV and so. Never have i tried 510's or 801's becouse i felt that the 901 was working great for me. Not saying i wouldnt like to try them, its just once u have something that works for its hard to switch up and change...., I just stuck with it~