The Bajaj Chetak uses a Keihin pb 20 model carburetor. This carburetor, as of 2012, is also used on the Kawasaki KLX 140 dirt bike. But you should rarely need to replace the carburetor itself, as most carb problems can be solved by disassembling the carb and spraying all parts, ports, and jets with spray carb cleaner.
Photo credit:bajajrestoration.blogspot.com
Photo credit:bajajrestoration.blogspot.com