I'm not saying do it this way, you can disconnect the fuel line at the pump and use a squeeze bulb to send a air back into the tank. The pump is just two bolts and two fuel lines in and out to remove. You should be able to pump the shoe that rides on the cam and get evidence of positive pressure output.
My route is based on repeats of the same problems and using that education to deal with the usual suspects. Dirt, rust, water, and varnish in the gas tank can really cascade into all sorts of problems.
