Changed fuel filter today,tractor will not start. Tractor starts with a pull from truck.Runs ok,but when I turn tractor off, will not start back up.This is a Montana 4940C. The hand pump on the top of filter appears not to be working,so I do not know if I have removed all air in fuel system! I ran tractor for 30 min.thinking I would get all the air out,did not start back up.It is like the fuel on shut down is returning to fuel tank and being replaced with air!! Any Ideas??