Ply and Burl

Several years ago, I taught myself to knit Continental style (I had done English up to that point). Early on, the tension on my knits and purls was about equal, probably due to my lack of dexterity and thus the extra-tight grip I kept on the knitting. However, while I knit quickly and easily in Continental style, my purl stitches seem to be getting really loose. Substantially looser than the knit stitches to be sure. I’m not sure why this is — I’ve tried correcting it by using an extra wrap around my fingers to increase tension, but it only helps marginally. Thoughts? Ideas?