I was running dual carbs on a 261 without heat for several months, then finaly got around to plumbing in the heat. First thing I noticed with the heat was that the mixture was way too rich, but was previously fine without heat. Now I've leaned both carbs I'm convinced that the engine runs better heated, idles a little smoother than before, and has a higher vacuum signal. I'm in Northern California and it doesn't get very cold here. Always experimenting.
Don.