I have searched the internet but can not find the answer.  All web sites
state a "normal" engine's vacuum, at idle, is ~ 17 to 21 inches at the
intake manifold. But, all these examples are for cars with one manifold
connected to at least four cylinders. I am trying to diagnose a flat four
with four venturis and individual intake manifolds. When I  attach the
vacuum gauge under a single venturi it produces rapid swings from zero to
20. Do I need to connect all test ports together to smooth these readings
out or is this the problem?
TIA
Ken