Have you done what edyle suggested? Empty the tank, wash it out and put in a new coil?
Once you've done that, start low and work your way up. Generally you can take the resistance of the coil and add two to get your voltage. So if it's a 2 ohm coil + 2 you'll be at 4 volts. Using a fully charged battery (4.2 v) you'll be around 7 - 9 watts. When I used clearos with factory coils I generally vaped at 7 - 7.5 watts. Above that I would get burnt hits.