dual coil NOT sub ohms..

[chykensa]

chuxsta - Nine times out of ten, leaking problems on Kayfuns are due to the wicking. Do you use cotton wool or rayon? If you are using CW, make sure you are giving the wool sufficient space to expand when it takes on juice, but enough to fill the coil comfortably. If using rayon, it needs to be tight enough in the coil that the rayon 'squeaks' when you move it from side to side; rayon does not expand so you can afford to use more of it and not cause problems.
Another factor is the ohm rating of the coil. I personally find that Kayfuns work best with coils of between 1 and 1.4ohm, and exclusively use microcoils now.
Finally, what power are you using with it? Although not a hard and fast rule, something around 11 or 12W seems to hit the sweet spot for me, and if I drop the power too much it starts failing - I suspect it is something to do with the speed at which the juice is being vapourised and thus setting up the vacuum which is fundamental to the way a Kayfun operates. If the vacuum isn't present, then there is nothing to stop the juice from leaking around the airhole; with a good vacuum, everything is leak-free, and you can lay down a KF on the table for hours without it leaking.
Final thought, carefully check all the other 'O'-rings - it may be a small nick in another ring which is allowing the air in and preventing that vacuum.

I'm sure that others will chip in with their suggestions, but I feel confident that between us we can get you using the KF successfully