Idle drops during warmup/stall!

This sound familiar,.. ??

Car starts well, you back out the driveway, come to first lite,, it's fine,, come to 2nd lite, it stumbles and dies,, instant restart,, come to 3 rd lite, it stumbles,, may/may not die,, and runs fine for the rest of the day.. Happens for 3 weeks to a month every year,, spring and fall..

It's icing,, if you adjust any screws,, remember where they were cuz it'll need to be set back in a few weeks..

To prove it,, At the same hour, take the top off the air cleaner, start engine,, and with flashlite,, look down the throat of the carb near the throttle plates, and watch frost/snow form around the inside of the carb base sufficient to plug the idle port, and transition slot,, closing off the flow of fuel.., when the snow melts,, the car will resume normal operation..

Things like stuck/no heat riser, plugged heat cross-over, contribute to this condition,, I tell folks to live with it the few weeks it happens, because the cost of repair can be expensive..

hope it helps