Any chance you have less than half a tank of fuel?
Turn your gas petcock to reserve, pull the choke and give it another try. It sounds like you have all you need for it to run and it fires when you spray starting fluid into the carb, so try this and see if it fires up.
The "ON" position only works when you have almost 6" of fuel in the tank. There are two pickups in the tank. The "ON" pickup tube extends almost 6" up into the tank. The reserve one is open at the very bottom o the tank. Once you get below the 6" mark or so, you have to switch it to reserve or you won't get fuel. It looks like there is plenty of fuel in the tank, but won't run.
Maybe not the problem, but worth a shot.