Using 80 VG or even 70 is going to be thick and even if you think you primed the coil does not guarantee it is. The cotton is packed in there very tight, not to mention there is a fiber wrapping around the exterior of the wick.
Once you get that metallic burnt taste, the coil is no longer good, you will not recover it by adding more liquid thinking there was just enough to avoid a dry hit. Plain and simple, you burn the cotton, you just killed it.
Now how to avoid this. Get a new coil and use a needle to pull out and loosen the cotton around the ports, you can even push the needle completely through to the other port, just being careful to avoid hitting the vertical coil. Keep in mind that on 2 of the ports there will be a metal sleeve like that actually is a slot to hold the wick in place so you will not be able to work a needle in those 2.
Use the 50/50 for the priming. I actually just pour liquid into a tea cup and literally dump the entire coil in it to soak for a few minutes then wipe it off then shake it out like you need to get more ink into the tip to write.
These coils are notorious for popping, crackling and spitting and very little you can do to avoid it, however turning the power up to 30w and using a longer drip tip can help this issue.
