The fuel tank may also have a screen filter in the fuel inlet in the base of the tank where the hose feeding the carburator connects to it so that should be checked as well.
If you are sure it has no fuel entering the carburator the tank should be removed, the gas dumped out and the fuel inlet removed and the tank cleaned with marbles or pea gravel and some hydrogen peroxide to break up the dirt and then drain it out and then put the inlet screen back in and remount the tank and put in fresh high octane gas.
I have been the victim of a plugged inlet screen killing a riding lawn mower completely and it was only corrected after doing the surgery described above to correct it.