Idle drops during warmup/stall!

1965 Valiant w/273 and 2bbl (stock)

Starts up nice and quick when the car is cold but within a minute or two of driving the idle speed will drop to around 400 rpm and threaten to stall or will stall completely! As long as I am moving the car drives fine and it will go away when it starts to reach operating temperature.. It started doing it intermittently a few weeks ago but now it does it every time I go out!

Do I just need to adjust the choke a bit? or is it more serious? (Cannot go get it tuned for another week or two..)