There is some good information here
http://possumjimandelizabeth.com/xht...g_sing401.html.
Are you certain this is a timing issue? Is the machine stitching? If it is stitching, do the stitches look off? This might be a tension issue.
These older machines are pretty tough and very reliable. The only time I've had a timing issue was my own fault. I used hand quilting thread which has a glaze. It didn't take long for the machine to be throw out of time.