I very rarely get a faint burny taste with blue foam and when I do and check the problem is usually that my blue foam has slipped in and isn't even contacting the atty (i.e. so it's not the blue foam I'm tasting but rather lack of
juice on the atty). When the blue foam IS touching and it doesn't taste right, I top off and if that doesn't help I do a full fill (i.e. remove foam, fill cart 1//2 way with juice, press the foam into that then work the foam back up into position using a smooth tiny unbent paper clip, then top off if needed (usually is).
If it still tastes funny then either it is time to clean the atty or time to clean the foam or both. This weekend I needed to do both after using both all week (especially because I used some juices with oil-based flavors like citrus and I also used a super-thick VG a couple of times).
I have never ever gotten a taste from any of that as bad as burning polyfill (white) stuffing.
My cleaning methods...
blue foam - hold a corner tight and rinse under running water then pat dry with paper towel
cart - rinse under running water and shake out
atty - soak in vodka (grain alcohol from liquor store would be better). I soak overnight in a jar of vodka after making sure all trapped air is out of the atty. I swish occasionally. Next day I swish, scoop some alcohol through it to rinse out dissolved stuff, shake it out well and set on paper towels to dry for days until I need it (meanwhile I am using the previous week's clean dry atty after priming). if I needed it right way I would use blow dryer or blow through it until it is dry.