So I recently picked up a new KR808 from myvaporstore.com and love it, but since i did I gave my 21st century e-cig to my buddy and after a few weeks he noticed that some of his cartos that have been refilled are becoming impossible to take a drag on, even a freshly refilled one. I mean talk about sucking a marble through a straw to get a slight vape, any ideas on what's wrong? My guess is the carto burnt out, or maybe needs a good boiling