It seems that there are variations between combines in production. On my 750, there is a sediment bowl threaded into the bottom of the fuel tank. Some of these have a fine screen inside, right above the glass bowl. On my 750, the fuel line from the sediment bowl, which has a shutoff valve that must be fully open, feeds the electric fuel pump, mounted on the fuel tank bracket. The mechanical fuel pump is mounted on the rear side of the engine. You check the mechanical fuel pump when you bleed your fuel filters by pumping the lever on its side. If the fuel pump cam lobe is at its highest spot, you won't be able to get any action until you rotate the engine off its high spot. There are also screens inside the mechanical fuel pump, which you can get at by taking the top off it. Check the diaphram while you're at it. A lot of 510s came without electric fuel pumps and had fuel starving problems that were solved by adding an electric fuel pump. When you turn your key on, the electric fuel pump should tick quickly at first and then slow right down. If it keeps ticking rapidly, you've probably got a hole in its diaphram. Don't forget to check that your fuel lines are clear. Disconnect at both ends, and blow out with compressed air, checking for decent air flow in the direction the fuel moves.
