Plugging during winter

[geezer#99]

Block heater won't help your situation. Your heat riser under your intake is likely stuck or non-existant. It takes awhile to warm up the intake so the fuel vapour in the intake stays a vapour. A cold intake causes the fuel vapour to revert to a liquid. Once you build enough heat in the intake it runs better.
My 230 in my old 65 did the same. Had headers and no heat to the intake. Took a few minutes to warm up and then after driving the first 1/2 mile it would start to run like crap again cause my air cleaner had no warm air supply to it. It would warm up again in the next half mile and be good from then on.
Check the heat riser.