How long have you been using the current coil?
What's the resistance in the current coil and on what battery/
device are you using it?
Does the coil look somewhat clean if you remove the rubber cap and look down into it, or does it look burnt/dirty? If so, and/or the coil is more than 2-3 weeks old, it might simply be about time to change it.
Also, if it's screwed on real tight onto the battery/device, try loosening it a bit and see if that helps on the draw?