Clean the strainer in the fuel tank. That will involve removing the tap from the tank and cleaning out whatever crap is in there.
I usually use a shop vac in the filler neck to hold the fuel in, then remove the tap. You be carefull to adjust the shop vac so that it draws JUST ENOUGH air to keep the fuel up but not so much that it collapses the tank... It's really not that hard to do.
Also check over the lines to the pump carefully for leaks. Might be a cracked line that's allowing it to draw air.