Yes there is a fuel pump. g1g had a similar problem with his. Click on this link:
http://classbforum.com/phpBB2/viewtopic.php?t=628
There's a photo of an Onan with the cover off in that thread.
I don't know if there is a shut off valve.
The generator fuel line usually taps into the fuel tank at around the 1/4 tank level so the first thing to check is that there is enough gas in the tank.