1989 Mazda 323 1.5l SOHC carb stalls and hard to start

1989 Mazda 323 1.5l sohc carb, 190,000kms, it stalls on cold starts and hard to start only when cold, auto choke do you think? And how would you fix the choke if that was the problem? Also have a heat light on the dash which pops on sometimes. It only comes on when vehicle is warm but the cooling system temp gauge reads correctly (in the middle) so the cooling system seems fine, car doesn't seem to overheat, so maybe this is the exhaust heat light? Does that mean it's a new oxygen sensor? The light only says "heat" with a picture of what looks like a tube with a bulge in it(best way I can describe it)
thanks, Mark