…there was this attachment you could buy. These instructions have a manufacturer address with a postal zone, and those were replaced by ZIP codes in 1963, so that plus the mid-'50s car profile gives some idea of the era. Looks like a close ancestor of the 3-nipple fuel filter used in the Ultimate Xtreme Stage-2 version of the fuel line mod: a chamber for vapour to be separated from liquid fuel, and provisions to send the vapour back to the fuel tank. My best guess is that inside the can, the inlet from the fuel pump is near the top and the output to the carb is at the bottom, and there's a small orifice—maybe 0.045" or so, like the one in the 3-nipple fuel filter—in the vapour outlet. The saddle clamp for the fuel filler pipe reminds me of the quick-'n'-dirty ones used to tap into a cold water line for an icemaker or whole-house humidifier, or the puncture-type side taps for cans of refrigerant. I learned of this item from a blurb about the 1973 AMC police cars; its mention made me go looking and I found the instruction sheet. Don't know that the kit used by AMC was the same as the older kit in the instruction sheet, but seems plasusible.
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VaporTaker_1A.jpg [ 223.7 KiB | Viewed 2961 times ]
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1973 Police Vehicles-01.jpg [ 255.44 KiB | Viewed 2961 times ]