[Tom Vaught]

Going to talk a bit about Holley Throttle Linkage Levers today.

Knowing how to quickly recognize a Chebby carb from a Ford or Chrysler Carb at the swap meet helps in the Bargaining Process.

It also helps you understand the Positives and Negatives of the linkage.

The first carb we will talk about is a carb you will find a lot of times at the local swap meets. See "Vacuum Linkage" Picture.
It is a "Chevrolet Style Carb" and has Vacuum Secondary Linkage. The linkage that you see on the right side of the picture shows the Positive Closing "Link and Slot" system. When the Primary Lever closes the Primary Throttle Blades it also pulls shut the Secondary Throttle Blades. The link between the two levers makes that happen. A "Vacuum Secondary" Carb

The second linkage shown is again Chevrolet style linkage but designed for a 660 "Center Squirter Carb" or some of the very old 850 cfm Tunnel Ram carb applications. See "Double Hump" Picture.
It is called "Double Hump" Mechanical Linkage because of the visible "double hump" in the slot portion of the Primary Throttle Linkage lever.
The Linkage goes to a given point on the Primary Blades of the Primary Shaft and then opens all of the Throttle Blades quickly from that point until WOT of the carb.

The next picture is an example of the "Single Hump" Tunnel Ram Linkage. As you can see in the "Single Hump" Picture the Primary Throttle Blades can only move a few degrees before the Secondary Blades start to open. A "Race Only" linkage for most people. You can drive a engine on the street with this linkage but gas mileage will be poor as every time you touch the throttle 4 Accelerator Pumps are dumping some fuel into the intake manifold.

In this picture: "Jerry Rig" the "Operator of the Vehicle' has "Jerry Rigged" an factory Chevrolet Style Vacuum Linkage "Throttle Return Linkage" to act like a poor mechanical secondary linkage. Massive hesitation with this set-up on acceleration.
In the Old Days you could buy a Carb Squirter with 4 squirter nozzles (2 extra long tubes extension nozzles added on a regular Primary Shooter).
You drilled a couple of holes in the choke housing, stuck the "extended tube shooters thru the holes" and hoped the accelerator pump fuel went somewhere in the secondary barrels. Without the secondary fuel this carb will have a big secondary throttle hesitation with any throttle movement. Some people used a sheet metal screw part way down the slot that worked much better vs this crappy tie-wrap design.

In the final picture, "Johnson Linkage" you can see the mechanical linkage to open the secondary barrels using a very complicated "Pivot Cam" like a "Center Squirter Cam" uses but turned sideways with the "roller" on the top. Lots of pieces and cost but it was designed by a Holley Carb Chief Engineer so it must have been PERFECT and therefore went into production. $$$$$$ It Works Well though!

So now you have the typical linkage systems you will run across on the carbs you will find at the swap meets.

Tom V.