Deere did have a cold weather gas manifold, were the exhaust channel runs over or under the intake channel rather than behind it like we are used to. But no heat exchanger valve like the numbered series. I am wondering what is blocking the intake path pre carb to put the system under that much vacuum to frost the carb and manifold. Maybe dissassemble the air cleaner and soak the wire mesh air cleaner then wash out. Or for a quick test turn the 2 bolt pipe from air cleaner to carb upside down and put a paper element on like the pullers do and see if problem happens that way.