New atty's need to have the primer burn off before they'll start tasting right, If not new and they're already broken in, whenever the atty gets dry, you'll taste.smell the atty burning, yuck! The bottom of your cart can actually start to get hot. I've heard of 510's actually melting their cart because the liquid ran out. But 510's burn hotter.
As long as your cart has liquid in it, and you make a habit to lay your e-cig down when it starts getting warm, it should be fine.
Anyways, that's the only times I've ever tasted that burning taste.
Note: I'd use a new cart, that odor may have absorbed into the cart's filling-ugh!