1984 Oldsmobile Toronado stalling

My Toronado runs great after it reaches normal operating temp. However, after the choke has opened, (3-5 minutes), it starts to stumble and stall - sometimes it will die. It will re-start easily. The problem usually persists for about 15 minutes. It has new ignition components and there don't seem to be any vacuum leaks. I don't suspect fuel delivery blockage because the stalling goes away after warm-up. Any ideas?
Thanks