We bought a 9760 and are about to run it for the first time. We have a 635 head (also new to us). Says in the book that variable speed feeder house needs to be on slow speed for grain platform. I really feel dumb but for the life of me I can't figure out how in he11 to slow this down or speed it up (appears to be slow now) but I'd like to know how to operate it. Can anyone help me out?