update: I siphoned the fuel out of the tank, then swished the remaining fuel around and poured all the fuel into a jar through a coffee filter. No sediment. Poured the fuel back into the tank. Installed the new carb. I have now cut the entire lawn twice with no stalls. If i get onemore cutting I'll call it a solve. I plan to disassemble the old carb and see if I can sleuth out the problem.