Assuming you have the juice control opened sufficiently, you probably have an air lock situation. Similar to a carto where you might sometimes have to do a couple of dry pulls to get the juice flowing. Unfortunately that trick doesn't work so well with the Killer.
Basically, you need to somehow release the vacuum that can build up in the tank. The Kir Fanis tank I'm using has a fill screw, which is handy. Simply taking the screw out for a few seconds gets the air pressure settled, and the flow going nicely.
I tried a couple of things to see if there was another way to accomplish this on a standard tank. What seems to work is tilting it so that the holes that feed the atomizer are out of the juice, and then doing a couple of sharp dry pulls - you want to use some paper towel or something over your drip tip so you don't get juice in your mouth because chances are you will get a little otherwise.
Hopefully other folks will have some suggestions. Once the air pressure is set, it wicks well, and works fantastically. It should be set for the rest of the tank.