Reduce the air flow and drop power.
First off, if the coils are getting black, you are burning the sweetener in your juice. This builds up and causes a funky flavor. Solution is reduce air flow and use lower power. Which by the way, will give you better flavor. Airflow is for clouds, not flavor. For example.. I am running a dual coil on my Tsunami. I run at 130w at half air when puffing for flavor, but 200w and full air when going for clouds. Your inner coil will get gunked faster than the outer wraps because that is where the heat is. The outer wraps do not provide heat, they take heat from the coil and trap juice.
Kanthal and NiChrome are considered resistance wires, they have higher resistance so they heat up faster when current is passed through.
Stainless steel, nickle, titanium are conductive wires, they allow current to pass through more freely and tend to absorb heat quickly (which is why they use these materials for heat sinks in electronic soldering)
So basically, it is all about finding the balance you like. huge clouds OR huge flavor OR medium cloud and flavor...
Clouds<-----------------------------------------------cloud and flavor -------------------------------------------------------> flavor. The more you have of one, the less you will have of others. Which..is where power and airflow come into play. Less air = thicker vape and more flavor, and less power is so you don't burn the cotton.
edit.. By the way.. cotton is cheap. When your flavor gets funky, toss the old cotton, dry burn the gunk off your coils, put in fresh cotton, and vape on.
