If you are pulling to the left, then your left cutters are cutting more than the right. This could be because the lefts are sharper, or the rights are shorter (different lengths), the lefts have a greater angle, the depth guages on the lefts are lower.
I have this problem occasionally on my stump saw, when I rock it badly. It can take 3-4 filings to get it straightened out again.
My suggestion is to look at the teeth and see if they are about the same size and angle (use the index line as a guage) and then file the lefts (right hand) about 5 strokes and test it. If it starts to improve, then try 10 strokes on the left and 5 on the right.
When I file, I use two hands on the rights (left hand filing) and only one hand on the lefts (right - dominant hand). Also I file the rights first, so I'm slightly tired and cramped when I do the lefts and don't file as deeply. Also if you need to use glasses to read, use them to file.