What liquid are you using? If it's heavy on the VG, it probably won't wick fast enough. Another thought is your voltage. New coils seem to need a break in period--especially if they're flaky out of the package which happens all too often--so I always try to remember to turn my voltage all the way down when I put a new head in and gradually turn it up to whatever tastes best to me.
Have you tried soaking the used heads in vodka or everclear, then rinsing and let air dry? I do that any time my vapor production drops or they start acting up--misfiring, not firing, taste off, etc. I also do the drunk soak and rinse on a new coil to get rid of the machine oil taste some new coils have and after a dry burn to get rid of the burnt silica taste. If you've got older Kanger coils and managed to burn the rubber insulator--it's a goner. Newer coils have a different material for the insulator band so I haven't had that horrible burnt rubber issue recently. Anyway, try the soak & rinse. You might also try dry burning if gunk has built up on the coil. Search youtube for videos that show you how. It's not hard or overly complicated but taking the tiny buggers apart is hard to explain. Best to watch a few videos to figure it out.
Have you tried soaking the used heads in vodka or everclear, then rinsing and let air dry? I do that any time my vapor production drops or they start acting up--misfiring, not firing, taste off, etc. I also do the drunk soak and rinse on a new coil to get rid of the machine oil taste some new coils have and after a dry burn to get rid of the burnt silica taste. If you've got older Kanger coils and managed to burn the rubber insulator--it's a goner. Newer coils have a different material for the insulator band so I haven't had that horrible burnt rubber issue recently. Anyway, try the soak & rinse. You might also try dry burning if gunk has built up on the coil. Search youtube for videos that show you how. It's not hard or overly complicated but taking the tiny buggers apart is hard to explain. Best to watch a few videos to figure it out.