Night before last I started up my '63 Corvair and heard a strange, new sound like a rattling exhaust. As soon as the engine came off idle it went away. Yesterday, in the daylight, I took a quick look-see under the engine lid and discovered the choke kick-down had broke. Second one in the last six months, but since the parts are forty-some years old, I'm not complaining. Last night I pulled a replacement part off a spare carb and swapped it with the bad one. All's good this morning - no bad noises. I guess that side wouldn't idle with the choke open and the engine cold.