I've had a small number of mega carts not work like they're suppose to. I fill it up with juice, but besides of getting vapor, I get smoke, and it smells like the fiber that's inside the cart is burning. I've had three, maybe four of them burn like that. I doubt it's me overfilling them, because I've done that on a couple of others and they work just fine. Is there away for me to fix the problem, or is it just a case of bad mega carts?