Follow where the feed dogs attach, down and under the machine. There should be a linkage that you can adjust under the machine. It just may be very hard to get to. I've had several machines that the feed dogs either scraped against the back of the plate or banged it rather hard and that adjustment to the linkage was key. I've never worked on a 834 that I remember, so the service manual that Joe recommended would be handy for you to have if you can get one.