Intake differences?

Back in the day on my Torino (sorry!) with a mildly built 400 I used to have ice build-up form in the primaries when warming it up. I was wondering why the engine would fire right up after setting the choke with a single pump, idle high (about 1400 rpms), where it was supposed to, then just stumble and die. I pulled out a flashlight one day and took a peek. Frost was blocking the idle mixture transfer slot and hole and seemed to be growing right off the throttle blades.

Keep in mind that this was Chicago in the middle of winter, the humidity was high and the temp I think was in the single digits. I was young and this was my daily driver. This particular car had a Holley street dominator single plane with the heat passages blocked off. The following weekend I replaced the intake manifold gasket to unblock the crossover and the problem was gone.

I'm guessing that the problem was caused by a combination of factors:

1. It was really freakin' cold!

2. Chicago is on the shores of Lake Michigan so it's really humid.

3. The air compressing at the top of the throttle blades and rapidly decompressing underneath them was working like an air-conditioner.

4. The addition of fuel to the air causing further heat loss.

5. Finally, lack of manifold heat to thwart all the above processes.