There are really only 2 reasons a Clearomizer may taste burnt.
1. Dry/ poor wicking
If you vape it till it is empty or near empty the juice may not be making it up to the coil and will give you dry/burnt hits. As the clearomizer gets low you may need to flip it over once in a while to help keep the top of the wick saturated with eliquid. Or you can just refill the clearomizer when this starts happening.
If this is a new or freshly cleaned clearomizer, make sure you primed the coil after you filled it. If you have and after a few draws it starts to taste burnt again then the issue may be in the inner cup seal of the clearomizer. It may be pushed in too tightly and pinching off the wick so eliquid can not make it to the coil, or the seal is not in straight and the notches for the wick in the bottom of the seal are not over the wicks right and they are pinching off the wick. You will need to adjust the inner seal to fix this issue.
2. Dirty clogged
If you have used the clearomizer for a week or ore you may need to clean the clearomizer, as over time sugars from the eliquid will build up on the heating coil and can cause a burnt flavor. To fix this you will need to either clean the clearomizer or toss it and replace with a new one.