Try the dangerous route....run a hose from the fuel pump inlet to a small can of gas and see if the pump will draw from that. If it will, the problem is in the lines/valve/tank. If it doesnt pull, the problem is in the fuel pump/line to carb/or carb inlet.

Be careful, gasoline vapor will ignite!!! Liquid gasoline will not burn but it's darn hard to get rid of the vapor layer on the surface!!!

mike in tucson