The bad taste can be from the primer that comes in the atty. If you don't already know, it is there to prevent damaging the heating coil when it is first used. Add a couple of drops of
juice, then take light puffs to burn off the primer. Repeat this process until the flavor comes through as it normally does.
If that does not fix it, it could be the coil is burned up from lack of juice or primer and then the bad taste may always be there. I have had this happen and it never went away. On another occasion, I soaked the atty in vodka overnight, then dried it out and primed w/ 3 drops of e-juice. I then broke in the atty again using the steps I listed in the first paragraph. It works fine today.
You can return to TW if you did not buy in bulk and the taste never subsides. I had one 4081 atty that I bought a few weeks ago and it tasted like burning metal from the start. I tried the steps listed above before exchanging it and the new one had the same issue. I eventually wrote it off to a bad batch of attys. Everything I have read up to now leads me to believe that most of the time e-cigs work fine but their components are disposable over time. However, sometimes you will receive parts that are DOA or don't work very well. I would try to purchase from suppliers that have return policies and good customer service. Hope this helps.
EDIT: I was disgusted by the burned taste, especially the metallic aspect of it. I would not recommend inhaling anything that tastes/feels wrong. You should be able to puff and get a taste of the vapor w/o inhaling. Use good judgement is all I can say.