There are many places in the forum where you can find information about burnt taste. First, you have to get out the juice that primer the atty's. Then, you need to be sure your cartridges give enough liquid to your atty, so your atty can wick well. Also, you need to know that when an atty is becoming dry it gives a couple of burnt tasted draws. If you are using cartridges with this problem, you may use a cartridge mod, take a look to
http://www.e-cigarette-forum.com/forum/cartridge-mods/70962-my-simple-cart-mod.html. To be sure the problem is in the cartridges you can drip a few drops directly into the atty and then use an empty cartridge (without the filler) to take a few draws. If you don't get a burnt taste in the first couple of draws, you have a wicking problem. Before, you need to be sure there is no primer.