Ruined a perfect day at the lake yesterday as my 1996 Yanmar 2GM would not start. Cranked fine but just would not fire. It ran flawless 3 weeks earlier after sitting for the winter. My first thought was air in the fuel system. I bled the system like I do when replacing fuel filters. Use the pump manual lever to get fuel from vent at secondary filter vent. Then cranked engine with cylinder relief valves open and water pump belt off. Usually one or two tries and it starts. This time no go. Went through same bleed procedure again and I noticed the manual pump stokes did not deliver fuel to filter vent but still getting fuel to vent when I cranked with cylinders unloaded. Then I cracked the lines at the injectors, which I have never done before, and never got any fuel there. I replaced secondary filter although it looked clean. I opened secondary filter and there was a little crud in the bottom, but filter looked good but did not have a replacement. Also cleared external tank vent which was somewhat blocked with spider debris. So..(sorry for long post)...looking for any help. Thinking maybe the fuel pump.