I was recently talking to some friends of mine that are very good mechanics, and they said that with me running an open element, I was going to play heck trying to open the secondaries because of the lack of vacuum inside the cleaner assembly.

Does this have any truth to it in regards to our cars?

BTW a search turned up nothing relevant.

 

I doubt it has any truth in regards to any car. The vacuum secondaries are operated by venturi vacuum.

 

What is venturi vacuum?

 

Vacuum secondaries don't feed of air housing vacuum. They feed off a small venturi pickup that feeds to the primary venturis. There is also a venturi tube that feeds to the secondary venturis. Then there is the secondary diaphram chamber with an internal spring that keeps the secondaries shut at idle. As vacuum is increased through the primaries, it is picked up by the venturi tube that leads to the secondary diaphram. This vacuum begins to pull up on the internal diaphram spring which in turn cracks open the secondaries. Now there will be a vacuum signal through the secondaries as well and is picked up by the side of the pickup tube that leads to the secondaries. As throttle position increases (go more and more to WOT), vacuum through the venturis increases. As vacuum increases, the diaphram gets pulled up more and more which opens the secondary throttle blades. Not too sure there's too much air cleaner assembly theory in this.

*edit* As the engine operates, it sucks air in through the venturis. This movement of air is venturi vacuum. How fast the air is traveling, or the load on the engine, determines the strength of the vacuum signal.

 

Thanks for the great explanation Stekman!

Thanks guys for answering my question!

 

Your great mechanic friends have lots to learn about holley vacuum secondary carbs and air cleaners.
Don't think in terms of intake manifold vaccuum.
They do not work that way.

Think in terms of airflow through the venturris creating a vacuum signal. This vacuum signal that, also causes fuel to flow from the fuel bowl into the manifold, is what controls the secondary throttles by acting on the diaphram against spring resistance.

The spring in the diaphram housing does not close the throttle.
It just resists opening. The combined throttle linkage and return spring close the throttle.

A engine that needs the extra airflow will open the secondaries all the way.

 

Thanks FBird!

Strange he would say something like that, something that is so off from the truth.

Thanks again guys!

 

In my experience, mechanics are about the worst source for information about how things work.