Gravity flow from the tank should be a steady stream so look for a blockage right at the tank outlet. You will need to empty the tank, then remove the fuel shutoff at the tank. There should be a replaceable filter screen attached to the fuel shutoff valve. Clean it, blow it out with air hose, or replace it.
The tractor should run without the fuel pump but the flow when the fuel gets low will not let it have full power. The fuel pump gives it full flow until the fuel runs out.