The burnt taste is likely your device not the juice, not sure what you are using but it doesn't sound very reliable! The juice is usually fine, but if you burn it bad enough and the juice sits on the burnt wick it can blacken the juice, and sometimes it picks up that burnt flavor and is ruined. Usually once I get a burn I replace the wick but I don't replace the juice I keep using it.
Also last time ive had an actual burnt flavor was using a Protank, I don't seem to get that crap with my KFL, my carto tank, or my vapeonly bcc with a rebuilt head