Drilling/widening channels in the kayfun is typically more harmful to your vape than in any way beneficial. If any modifying is going to be done it would be to increase airflow by drilling the airholes.
However, you don't have to do this to get a great vape out of a KFL. My guess is you are experiencing wicking problems/improper wicking placement. This is very important on kayfuns. Use a decent size diameter for your coil, and run the coil diagonal, in my opinion. You do not want the cotton wicking sliding 'loosely' between the coil. You want it to be a firm pull, but not too excessive. I wil typically trim the width of my cotton wick so the ends are not as thick (they will be less likely to block the channels). Then I wet each end of the wick slightly with juice and point them upwards, screw down the chimney base cap (make sure not to get any wicking stuck in the threading while you do this), and you should have two cotton wicking ends sticking up. Cut them off right at the top. Wet the coils a little to eliminate fray and allow for more control. Take a small screwdriver and position the wick on each side so that it is pressed down against the long base of the positive post. Take the mini screwdriver and firmly press the cotton against the posts and AWAY from the channels. Keep an end of the wick close to the channels, but not touching or covering it.
I remove my airflow control screw completely. I never get flooding or leaking. The increased airflow is beneficial.
Make sure when you are adding juice (I top fill), and put things back together, that your chimney is properly secured. I have noticed with kayfuns it fairly easily backs off of the threading.
Take bce22s advice and widen the diameter of your coil quite a bit, I have found this also to be more effective on kayfun style devices. But I'll say again don't toss the device just yet, your problem I am 99% sure is wicking. Pics of your builds will be helpful.
If you're using a regulate device shoot for 1.5-1.9 ohms. Ensure the cotton is not being choked inside the coil. Wet everything before putting everything back together.
As for the distance of the coil above the airhole, looking down other avenues like this, I recommend against it. With kayfuns I have found they are very finnicky and if you are having problems like yours, it is almost always a wicking issue. Sorry for the rant.
