It did it again, once the temperature dropped long enough below freezing. Battery charged and oil pan heated for several hours. Out to start and first open gas line, then choke out, throttle forward. Turned over, no start. On and on, varying choke and throttle. Finally a cough, a weak start that wouldn't take. Gas dripping out the bottom of the carb, and when turning over the engine I even see fuel coming out at the gasket line. A regular soaked spot in the snow on the ground below the carb.
Had earlier assumed that intake manifolds just too cold to keep fuel atomized on its trip up to the spark plugs. Still think that. Assume flooded situation, so wait. Come back and maybe a cough or timid start and silence. Shovel beckons for a snow clean up.
Over the summer: a carb rebuild--new needles, float checked out, new gasket, etc.
In warmer weather she starts up without any hesitation. This is why I think a heater plug inserted in the water intake elbow will work.
Tractor sits in a cold barn, a bit protected.