It appears these Walbro HD series carbs have two very small holes on the underside of the fuel pump diaphragm end of the carb, which I'm assuming act as an atmospheric vent. You can see them on the bottom part of the photo at the 3 and 6 o'clock position. These were pretty well plugged up, and I'm assuming that the sawdust gunk you can see made it's way through those holes over time, building up enough to impede the vents and not allow the fuel pump diaphragm to function properly, hence the flooding issue. Now it was only a matter of spraying this out and cleaning it up good with carb cleaner, and re-assemble. I've usually had bad luck not damaging the diaphragms and gaskets when tearing down carbs like these, they usually are pretty stubborn about coming apart cleanly, but this particular carb was cooperative, no need to replace them. After I got everything put back together the saw fired up and ran beautifully. It's funny, you would think a carb so gunked up like that would cause no fuel to be getting to the motor, not the opposite problem of flooding. If it's plugged up in the right place though, it will indeed flood the motor. One thing that sort of threw me off was the fact that the plug was dry and looked good when I pulled it, but I'm contributing that to the fact that I let the saw sit just long enough for the plug to dry off while I took a lunch break. Oops.
