The large rubber hose from the manifold going into the firewall was originally a route for the Hydrovac, that hose should go to the check valve and a second hose from the atmospheric side of the Hydrovac should go through the firewall to a round horsehair filter. Some of those items could be missing and we can't see the whole set-up.
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
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