Huckster, I had a similar problem a couple of years ago. I actually had to remove the shutoff lever on the fuel filter assembly and turn the nylon valve with a large screwdriver to get it to where the fuel would flow It was open just enough to allow the tractor to run at idle but it would not get enough fuel to run under a load or high rpms. WHat is happening is that the lugs on the lever are too short to fully engage the slots in the nylon valve assy. They disengage when you close the valve and will not reengage when you try to open it. Since you do not have to mess with the fuel filter very often it is not a big deal. Check that first before you mess with the rest of your system. A quick test is to unhook the fuel line on the inlet side of the fuel filter assembly and turn the key on. if fuel flows the problem is your filter valve. Don't forget to bleed the air out when you put it back together.
Good luck. I spent a couple of very frustrating hours before I isolated the problem. Willie Jones