Haven't worked on my 56 292 for a while, it's been running very well.  The past few times I've started it up, however, it dies suddenly (no sputtering or anything) after idling smoothly at about 600 RPM for a couple minutes. It starts right back up without even touching the accelerator. Runs about a minute and dies again. Started it back up again and ran it about 2000 RPM for a minute. Just sat there and hummed without a single miss as far as I could tell.  The engine is stock with a "teapot" carburetor and 56 distributor with points. Anyone have any ideas?