I'm assuming this fuel pump uses the engines vacuum pulses to move a diagphram back and forth, and that is what pumps the fuel. My Kohler uses a mechanical pump, while my B&S uses a vacuum type that bolts to the side of the carb, like yours. Have you made sure the fuel line isn't plugged? Have you replaced the fuel filter? If so, you made need to rebuild the pump.
check for a leek on the suction side of the pump. all pumps push better than they suck. a leek on the pressure will not leek but the same leek on the suction side will draw air, and no fuel. also i have the same tractor, and iam not impressed with the stock pump. iam in the middle of putting a electric fuel pump on.
Allis Chalmers 616 (Two) and a Kioti CK30 HST with loader and backhoe
Can you manually operate the pump to see if you can suck fuel through? The pump, if it's the one I think it is, operates by way of a push rod off the cam. I replaced mine with an electric one as the diaphrams went on it.
You say the pump is OK, so it seems more like a leak like the other posters said.