Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
ZD21F Kubota ? Twin tanks on unit. Have you tried to run out of one tank? I think yo have a bad suction tube in one of the tanks, and when fuel level gets to the bad section sucks air and lets engine die.
Sorry, just a single fuel tank, with a suction and return pipe. See if you can remove the fitting from the fuel tank , that goes to the fule pump. See if the tube going into the tank is damaged.
I see question is still open, did you get to check the suction tube?