The fuel pump is driven by pressure/vacuum from a hard rubber hose that comes from the crankcase. The pressure/vacuum created by the piston going up and down in the cylinder creates alternating pressure/vacuum in the fuel pump that acts on a diaphragm in the fuel pump. That is what drives the fuel.
If no fuel is coming out of the fuel line that goes to the carbs, you could have a ruptured diaphragm, a bad impulse line (the hose from the crankcase to the fuel pump), a plugged inlet filter on the fuel line in the fuel tank, or rotten pickup hose inside the fuel tank. I would also check to make sure there isn't a fuel shut off on the line from the fuel tank to the fuel pump.
Here is a simple test
Find the tank vent hose, remove fuel line from carb
Then blow into vent, see if fuel come out?
Then blow back on the fuel line,
If it goes back then the pump is bad!
But one other thing is the pick up in the tank!
I preach to replace all the fuel lines including the pick up in the tank
and at least take apart the pump and clean it or rebuild it!
Then clean the carbs!