You could have a cloged fuel filter, especially if you ran it out of fuel. Good chance you sucked up all the crap at the bottom of the tank.
You can check by removing the fuel line from the carb and connect some clear hose to it and run it into a coffee can or some other container. Crank the engine over a bunch of times and watch the can, if you see fuel your pump is working, if you don't see fuel running you probably have bad pump. If you get fuel then replace the in line fuel filter. Crank the engine and have someone look into the carb to watch for fuel, a pair of goggles is a good safety precausion. I dont think the 72 has a filter inside the tank but don't quote me on that, I could be wrong. If you don't get fuel after the filter change you prolly got crap in the carb.
Also, don't go crazy with starting fluid, a little goes a long way, that stuff is like super high octane. You don't want to damage anything. You can get the same effect with a little bit of regular gas.