Recently, when I'm bucking logs, and trying to make a straight cut at 18", my saw starts veering to the left, and I end up with 1/2 the log at 18" and the bottom half 15 or 16 inches. I'm no expert with the saw, but I have cut enough to know how to easily cut a fairly straight line. It just seems there is an issue with the chain or blade?? I'm also noticing more sparks than I would normally see coming from the chain in the middle of a cut. Eye sight doesn't show the bar to be bent, but.....? Whats the deal?