Check where the poly filler comes in contact with the atty bridge. If it's not melted or scorched then you might right about it not being the cartridge part giving off the burnt taste.
Do you have a drip tip or an empty cartridge without filler in it handy?
Drip 3 or 4 drops right on the bridge of the atty, pop your drip tip on or an empty cart with no filler back on and then try it.
If the burnt taste goes away with direct dripping then the filler just isn't making contact with the bridge and that wicking material under the bridge is getting dry on you. Fluff up the filler in your cartridge a bit so it makes contact with the bridge and try again.
Provided you have no flow problems with the cartridge...and you still get the burnt taste from direct dripping...then try cleaning the atty again.
If you have some everclear or vodka...soak it in that for a while then rinse with water. If not, water will do. Can try boiling if you like.
If all that fails...consider setting that atty aside for de-wicking and use a new atty with your carts.
If you de-wick an atty...it's great for direct dripping...but not so good with cartridges any longer.