When you "clean" them, whatever method you choose, make sure they are really dry. Sometimes this takes a few days, or a few hours. All depends on the method you use.
Another thing is to make sure any wick/coil/filler is really good and soaked and probably leave it sitting for at least 15 mins before vaping.
I have some times gotten the horrible taste, but mostly when I am being impatient and I vape through it!
It all depends on vaping style. Me and the hubby can fill up a boge carto and his will last him 3 days tops, while mine is going for weeks if not more. I dont take long heavy drags though, so I put less strain on the coil and very rarely ever get a burnt taste.