Same happened to me with the notch coil provided. after about a week it tasted terrible and the build up was too much for me to use it again. Been using hand builts ever since with pleasing results. My last coil build was on there for a little less than a month (with a few rewicks of course).I have to rebuild my Merlin today my notch coil I've had for over a week is starting to taste like junk. I was thinking about trying a hand wrapped dual coil. How well does that work? Also Does it fit with the air flow resistor in?
I have yet to use the AF restrictor, so I am not sure if it sticks out above the normal air intake. And I really don't know how much headroom is at the top there above the top coil. But, if you use smaller IDs (~2mm) you shouldn't have a problem sticking dualies in there.
The top coil (below) is 3.5mm and the bottom is 2mm. I wanted to make sure the airflow made it to the top coil. I think it will flow nicely around the bottom coil, though, no matter if they are both the same size.