I dont know if your tractors fuel tank has a siphon tube or a bottom drain .If it is top siphon type you may have just enough trash plugging the fuel line .On my Kubota it is top siphon and just a little trash in the tank and its a headache.It might run 20 minutes oe it may run a few minutes .Diesel Service fuel treatment or clean the tank is an only option.And have a new fuel filter ready.