Still chasing gremlins in the stock '54 Merc (with '55 teapot carb) and have a question regarding vacuum.  I have a new vacuum advance ordered and just checked the vacuum port on the carb to distributor and I am not detecting any vacuum signal.  I cannot get a reading on my test gauge nor can I feel any vacuum by pressing a finger into the hole.  I am reading 22 - 25 Hg from the manifold.at idle.  Is the signal to the distributor inherently low or do I have a restriction in the newly rebuilt carb?  Possibly with the spark control valve?   I have never monkeyed with a vacuum advance before and recently found that my current module is not holding any vacuum during a pump test but it does slightly move the breaker plate a bit with each pump stroke.

By design, the Teapot 4V carbs will not indicate a vacuum signal for the distributor at idle.  It’s a combination of ported and venturi vacuum at the distributor port on the carburetor with the spark control valve being a part of that mix.  If you speed the engine up beyond idle, you should be able to pick up a vacuum signal at that port.  The higher the rpm, the greater the signal but at idle, there should be no vacuum present at that port.

Lorena, Texas (South of Waco)