After about almost two months of
vaping, I have found that whenever I start to get the metallic/burnt taste I just need to give the atomizer cleaning.
I have a penstyle, so first I remove the batter and cartridge, then run very warm (but not hot) water from the tap over it, let it drain out, then fill it back up and blow
through it in both direction, and then fill it back up, cover both ends, and shake it back and forth for about 30 seconds, and repeat.
After that I set it on it's end (cartridge side down) and let it dry out. Two drips on the atomizer and then about 5 drops to top off the cartridge, and then I reassemble everything and let it sit for a couple minutes, just for everything to get reacquainted with itself.
Following this method I have always been able to get rid of the burnt taste.