I'm having a double portion of humble pie tonight. In my frustration with the fuel system, I started scouring youtube for information about pulse fuel pumps - trying to understand how they work and determine if that could be my issue. I found a vid of a guy pulsing air in the breather tube with his mouth, and (out of options) I decided to try for myself. Still no fuel through the system. Pulled off the fuel pump and blew on both sides to validate the check-valves and diaphragm. All good. At this point, I start to think there's a blockage in the fuel pickup inside of the tank. Looked under the seat and I saw streaks of grime on the chassis that seemed to be coming from the fuel tank fitting. Suspecting a leak, I pulled out the pickup and found that the seal that keeps it in the tank had corroded and split into two pieces. This was also allowing some fuel to leak at the fitting. And then... then it dawns on me. The mower was OUT OF GAS.
I dropped the fuel feed line into a gas tank and the mower fired right up and purred like a kitten. It all started coming together in my mind. Since the mower has been inoperable for so long, when it died while my son was mowing, my first thought went to all of the things that could have broken and I skipped right over the most obvious thing of all. On the bright side, I was able to discover a couple more leaks on the mower while I was troubleshooting. I also was able to change the oil, adjust the valves, replace the old valve seals and also learn a lot about how pulse fuel pumps work. So, now I'm waiting on the fuel tank fitting and grommet to come in the mail and really hoping that I'll be back in action.