I've had a Tobeco KFL from FT that I've tried using several times, and always found the draw on it terribly stiff, and it always found it's way back to the shelf in favor of better performing atomizers. Taking the base apart never revealed any obvious problems.
So yesterday, I brought it to work with me and decided to do some drilling. The worst that could happen is that it wouldn't work and I'd throw an atomizer away that I wasn't using anyway. I disassembled the base and clamped it in a vice. I decided to drill the air hole out to 5/64". IMO, that's about as big as there is room to drill for the KFL. Surprisingly, it drilled out very easily using a good sharp bit. I also added a little chamfer with a larger bit in hopes of killing any whistiling. To finish it off, I drilled out the drip tip to 3/32".
The difference is night and day! I've got a new toy with a great open draw that is working fantastic running a 2.2mm ID 26ga coil at .8Ω. It's now earned a spot near the top of VaPreis' daily vaping arsenal.
EDIT TO ADD PHOTO: