If I go over something you've already tried, please forgive me. I do not know what you already know.
The harsh throat hit with no flavor is an indicator of a dry hit. that is essentially when juice doesn't get to the coils. First off, if you take too many dry hits on the same coil, that coil becomes useless, since it will singe the cotton, and it won't be able to wick as good. If you've already had a few dry hits on the same coil, and it's not keeping up, then chances are, that is what's happening. Over time though, when a coil gets old, it is just simply time to replace it.
Now, the question to answer, is what caused it to get a dry hit in the first place. Ejuice is mainliy consisted of flavoring, nicotine, Propylene Glycol(PG), and Vegetable Glycerine(VG). The main two substances that affect the wicking, is the VG and PG.. which usually makes up a good portion of the juice. VG helps provide a larger cloud and has a smoother hit, but does not carry the flavor as much as PG. VG, however, is thicker, like vegetable oil, and takes longer to wick. PG, on the other hand, is a more water like consistency, has a harsher throat hit, and doesn't produce as much vapor... but because it has the consistency of water, it wicks easier. Take a look at your juice and see if it tells you the PG/VG ratio. If it has more VG than PG, then chances are, the atomizer has a hard time wicking the juice. The only thing you can do, is to poke a hole with a safety pin into the cotton sides to help the juice wick easier. A temporary fix to see if it is a wicking issue, is to put your finger over the air intake to block the air and take a few short puffs without the power. This move forces juice into your coil. I recommend doing this at the first hint of a dry hit.
I also recommend starting from scratch as far as the coils go. When you get a new coil, prime the coil. That means you put juice all over the cotton and coils until they are saturated.
This is a video with a very similar coil.
Hope that helps.
