Jake,
I'll bet if you look behind your seat you will see a tube coming up through the floor. It has a small air cleaner affair on its end. It's the breather from the atmosphere side of the hydrovac.
If you can't see it, you can hear it! With the truck shut off you can pump the brakes and hear it 'huff'.
If wouldn't seem like they would plumb this into the carburetor as it might tend to provide a little vacuum, and this side of the brake diaphragm is suppose to be neutral. Does this sound right?
Stuart
