Not to point out the obvious or sound too simplistic, but, if it tastes burnt and disgusting above 17 ~ 18 watts, turn it down.
Vape to your taste not to a number, whatever power level it tastes best to you is the right power level for you to use.
After the wicking material scorches / burns the only way to fix it is to prime a new head & replace the old one.
Sometimes the burnt nasty taste leeches into the remaining liquid in the tank, even if you replace the head the remaining juice can taint the new head with the funky taste.
If you know you've burnt it, best to dump remaining liquid & give everything a rinse.
Dark or colored and especially sweet liquids tend to clog wicking material, gunk coils and burn easier.
If you enjoy vaping liquids like this you will need to replace heads frequently.