did you pop the top off the carb and make sure the needle and seat valve is not stuck closed? You could have a couple of issues. If, when the carb was full adn float up at the top, the needle stuck closed, your carb could be dry now and not allowing any gas in. That would create pressure between the pump and carb. Then, if there is any junk that got in the pump, and is holding a check valve open, it would either not create the proper pressure, and/or drain back into the tank. I would at a minimum take the inlet line off the carb and make sure you can blow into the carb to ensure the needle is not stuck closed. Then, put a piece of fuel line on the line soming out of the pump and make turn engine over a bit and make sure fuel is coming out.
