About the coil :
If your cotton in your coil is burn out, you must to change your coil, and put a new coil in, otherwise you are going to have that burning taste in your mouth and the coughing every time that you are going to inhale from it !
The coils they don't last forever and after some use they tend to fade out, so after a while we have to change them with new ones, (plus sometimes it happens the coil to be defective from the factory) ! Every time that you're going to using a new coil, you have to put a few drops of e-liquid in, then put it in your tank, then fill up your tank, then let it down for some minutes (5-10) so your coil has the time to be full saturated with e-liquid so it can work properly !
About the coughing :
In the beginning we all had the coughing !
It's a stage that your body - organism have to adopt - pass through, because of the new way to getting your nicotine from smoking to vaping, after a while you are getting to use the new way and everything goes smoothly !
After some time, if you still have the coughing... probably it's better to find a deferrent type of kit ( a MTL kit that you can use it in less watts 10 - 15, and less air from your tank, or your e-liquid (your VG - PG ratio), or your nicotine level on your e-liquid !
For now i think it's better to watch a few reviews of your kit so you can understand the type of your kit, and how to use it more efficient !
If you have any questions - issues, hit us again !
(And again, it's just my opinion, and how i see some things, maybe someone else has a better answer, or he can explain better than me... !?
Yeah, my English aren't the best out there, but i think that you can get my point of view... !?)