Hello Brenda,
Take off the stop motion knob, put the 3 pronged washer in a different position, put the stop motion knob back on and tighten finger tight, tighten the screw in the stop motion knob and then test, if it still won't tighten take it off again and put the 3 pronged washer a different way even upsdie down.
Ken
drivewithken, June 2009