CB900C Custom 80-82. 4 kits - New K&L Air Cut-Off Valve Kits. Made in Japan. To prevent “afterburn” generated by a lean fuel mixture when closing the throttle, the air cut-off valve temporarily closes the slow-jet air passage, creating an instantly richer mixture.
I would only purchase K&L cut off valve and pump kits for my carburetor rebuilds. I wouldn’t go with anything else. Not only equivalent to OEM, but better, while also costing less.