There are four main parts to most ecigs...
1) Battery
2) Battery compartment
3) Tank
4) Coil
The #1 is the battery, and it's mainly just that..... a battery. Some come pre installed into a compartment and are not removeable.
#2 is the battery compartment. There are many that come with a permanent battery in it, or some where you can replace the battery. Some also contain electronics that can alter the voltage or wattage of the battery. Like I said earlier, many of them have a battery and compartment as one unit. In either case, it's the part where you push the button to make the Ecig work.
#3 is the tank area. It is the area that holds the juice. This can vary widely with each different Ecig, and some don't have a tank section at all (known as drippers).
#4 is the coil and wick. All ecigs to this day have some sort of wick to get the juice to the coils. The coils heat up, and essentially "boil" the e-liquid to produce steam (AKA Vapor) . This is the part that makes it all happen. Both 3&4 make a complete atomizer system. Yours is the aspire nautilus.
If you're tasting a burned taste, #4 is where it's comming from. Two reasons could be causing a burned taste... a) there could be buildup on the coils from the juice. When you heat the coils, it will burn some of that residue, and give you a burning taste. the other and most likely problem is b) the wick has burned some. If there's no juice to keep the wick wet, the coils get hotter than intended. This can burn the wick, and the wick itself can cause the burned taste.
You can try to clean the burned areas by boiling just the coils and wicks. Alchahol also helps to release some debris as well. I would try cleaning first before replacing the whole coil.
This is a picture of the Aspire Nautilus atomizer. You will see three parts in this picture. The one on the left is the wick and coil. It is screwed into the Tank which is the second item the third item is just a beauty ring to make it look better on your mod.
Once cleaned, you can determine what is causing the burned taste. Main "culprits" could be bad juice which leaves lots of residue on the coils, bad wickin, which could be from several reasons, adn 3, too high of a voltage. Without knowing your battery, I do not know if youc an even change the voltage/wattage. But again, I would try cleaning first. The first thing is after cleaning, see if you still have a burned taste. If you do, take the atomizer apart, wash it, then put it back in and sample a small ammount of juice to see if it still tastes burnt. If that still has a burned taste, you might just need to go find another coil to replace.
I hope this helps some. If I was too simple, it's because I don't know how much you know about vaping.
good luck, and vape on.