Thanks for all the replies. To close the loop on this . . . what a difference fresh (and real) gasoline make! The mower now starts up on the first (sometimes second) pull and runs great. When I have the time to watch it for leaks (this weekend), I will leave the fuel cut-off open to see if I still get a leak with the regular gas. At the end of the mowing season, I will likely overhaul the engine according to the wonderful suggestions here. It seems I need to rebuild the carb and replace the crank seals.