97 Big Bear 350 hard to start in cold weather

This is a recurring winter problem I have each winter. Trying to solve this before the winter comes again. I bought this a few years ago, rebuilt carburetor, new needle and seat, adjusted float height, idle air screw set at approx 2.5 turns. New fuel cock, inline fuel filter, valve clearances checked, air filter replaced, excellent compression. Starts great in warm weather, when down to 20 deg F or below, can be very difficult to start. I took the carb off, found the intake pipe cracked at the corners, replaced with OEM, and new oring. Reinstalled everything, starts fine in garage but I notice when it is running I can pull the choke out fully the engine does not die out like I think it should. Does anyone else have this issue? I removed the choke control, oring looked fine, cleaned out the ports for the choke again with carb cleaner. Same result. The maintenance manual I have is very vague on this. I have to leave it parked in my garage in the winter instead of the barn so it will start. This has one of those CV vacuum carburetors Any help much appreciated.