Vacuum Noise

[jdv69z]

302 in my Z runs great, but I am hearing a high pitched whistle while it runs. It is coming from the carburetor inlet; when I place my hand over the air horn, it disappears. Is this normal, or does someone have an idea what could be the cause? I have a brief video but it's 18.3 MB.

[L78 steve]

If its coming from inside the venturi area it OK. The engine is pulling air and fuel through the carb circuits.

[Z10Mike]

The Holley on my big block does the same thing.  More noticeable since I pulled off the cowl hood flap for full time cool air, providing a noise path.