The float bowl on every carburetor has to be vented to atmosphere, otherwise the theory of basic carburation wouldn't work due to positive or negative pressure occurring in the float bowl. You may not see a hole, but a port or stand pipe somewhere in the carburetor is allowing atmospheric pressure to act on the float bowl. carbking, did I word that correctly?

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy