Hi Victor and welcome to ECF.
I've only been using Cartomizers (510 Mega Cartomizers from Nhaler) for a few weeks now and I'm sure there are others here with much more experience, but this is what I've learned about them so far:
As to the burned taste, it seems it's almost impossible to get rid of once its there, but you can try a mouthwash soak and then rinse and dry them real good to see if that gets rid of it. I think the way to avoid this is to stop and refill the Cartomizer immediately when you think the fluid is getting low.
I've also run into a cartomizer with a "bad taste" right out of the wrapper. Nothing worked to fix that one so I've just put it away til I learn more.
Another problem I've had is a "hard draw" as the cartomizer is used over and over. Someone here recommended straightening a paper clip and carefully working it up the center hole from the battery end. For me, this worked very well to resurrect a Carto that had lost its draw. I also noticed that the paperclip may help with Cartos that have lost some of their ability to generate good vaper. With those, I gently rub the paper clip back and forth while its in there. If I see some black stuff come out, I rinse and dry it real good. After doing this, the vapor really increased, so I'm assuming the wire inside had become caked with gunk from previous burns like an atty does. I don't know how long this will extend the life of the atomizer, but its worked so far.
Be very gentle using the paper clip since you could break the wire in the Cartomizer. That would permanently end its life.
Hopes this info is helpful,
Rich