How does a 2x4 carburetor set-up function when progressive carb linkage is used?I'm understanding that the engine runs on the primaries of the rear carburetor then based upon throttle plate position of that primary carburetor and the connecting linkage adjustment, the primaries on the second carburetor begin to open.  Like a 3x2 progressive set-up, the primary throttle plates on both 4 barrel carburetors reach full open position in unison.
1) When can the secondary throttle plates of each carburetor begin to open?  Not until both carburetors are at the same primary throttle plate position so that both carbs have the same vacuum signal to activate the secondaries?2) Opinions?  For street use, does a 2x4 set-up with progressive throttle linkage provide more mannerly low speed stop-and-go operation or improved low speed throttle response?

Replies appreciated. 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

I am not sure about aftermarket setup's but the factory setup idled and ran on the primaries of both carbs. The secondary's were vacuum operated but could be set up to open mechanically by putting a screw in the secondary linkage. There was no way to set them up the way you describe with the design of the factory manifold. Try to idle on one carb and you will only get fuel to half of the cylinders.

All the dual quad intakes that were tested here at this shop have balance tubes or flow distribution ports between the front and rear carbs.  While the factory did synchronize the carb operation so that both carbs worked in tandem on the oem setups, the potential is there to do a progressive linkage for the carb operation.  If the carbs are mounted in a forward facing position, then you’d want the rear carb to be the primary carb.  If the carbs are facing rearwards such as the case on the early ‘Birds, then you’d want the front carb to be the primary carb.

Here’s a recent thread also covering this same subject.
http://forums.y-blocksforever.com/Topic107834.aspx

And here’s a link to the dual quad testing.  All these setups were tested with both carbs working equally.
http://www.eatonbalancing.com/blog/2014/01/17/y-block-ford-dual-quad-testing-on-aluminum-heads-part-ii/

Lorena, Texas (South of Waco)