My JD 650(1984 w/700hrs.) will lift the mower by itself while I am cutting. How do I set the draft control or get it to hold one postion? Under the seat I see a knob and on the side of the lift I see a small lever. I know the knob is for lift speed, but will it lock the lift also? What does the small lever do? Also the lift seems to be really sensitive when moving the lift control. Not much range on the lift lever.