Thanks Charlie.

 

See the little tube sticking into the primary venturi on the drivers side? That is the pickup for the secondaries. It is ported back to the secondary diaprgam along the top of the carb (you can see the ridge cast into the top).

As incoming air accelerates through the venturi the pressure drops (Bernoulis law). This pressure drop is sent to the secondary diaphragm and pulls it open. The beauty of the design is that it opens when the engine can use the extra airflow and not before.

When the accelerator is closed, the pressure rises in the venturi and the spring inside the housing on the backside of the diapraghm closes the secondaries. (there is also a mechanical stop on the throttle linkage that will pull it closed too (that's the one I mentioned before).

 

Venturi vacuum through tubes in the carb body, to the diaphram-spring / actuator rod at the rear of the carburetor, which then opens the secondary throttle plate.

 

Charlie, I may need to get a article on how carbs work. If there is no linkage how do the secondaries work?
Phil

 

I'll get a picture off the D-coder and post it to my site in the morning...remind me if I forget..*G*

If the description already provided serves your purpose, disregard...

 

The secondary linkage on the 4100 is on the same side as the choke. It runs from the rear of the carb (where the secondary diaphragm is) to the secondary butterflies. There is no manual connection to the primary butterflies.

The primaries must be opened to allow the secondaries to open. If yours will open without the primaries being opened then you have an unsafe condition. On the passenger (choke side) there is a small pin that pulls the secondaries closed when the primaries are closed. This pin prevents the opposite as well. Many times it is inadvertently left off creating this condition.