From what I've read in the modding forum, most of the time that burnt plastic taste is because all of the wire used for the coil and connecting the coil to the head is resistance wire. If you're vaping too hot for too long you can start to heat up the grommets that keep the wires from shorting out, causing that taste.
If you're feeling adventurous, you can get some new resistance wire, non-resistance wire and wicking matterial, then build a new coil that has non-resistance wires for the connecting wires, and resistance wire for the coil.
resistance wire is the part of the coil that gets hot and actually causes your e-juice vaporize. Non-resistance wire will still conduct electricity, but it won't turn red hot, hence hot heating up the plastic grommet that it is touching, and not getting that plastic taste.