Your Cart is Empty
If you've ever looked at an engine running two or three carburetors, you might assume they all open at the same time.
They don't have to.
With progressive carburetor linkage, one carburetor handles the initial throttle opening while the additional carburetor—or carburetors—come in as you push farther into the throttle.
For a street-driven multiple-carburetor setup, that can make a big difference in throttle response, drivability and fuel consumption.
Here's how it works.
Progressive linkage is a mechanical throttle-linkage arrangement that brings multiple carburetors into operation in stages.
Instead of every carburetor beginning to open the instant you touch the accelerator, one carburetor acts as the primary carburetor.
At light throttle, that carburetor does the work.
Push the throttle farther and the linkage reaches a point where it begins opening the additional carburetor or carburetors.
At wide-open throttle, the system reaches full travel and all of the available carburetion is in play.
In simple terms:
A little throttle = a little carburetor.
A lot of throttle = a lot of carburetor.
My 1966 Impala is a good real-world example.
The big-block Chevy uses two four-barrel carburetors. The rear carburetor is my main carburetor, while the front carburetor is the auxiliary carburetor.
When I initially move the throttle, the rear carburetor opens while the front carburetor remains closed.
The progressive linkage is adjusted so the rear carburetor travels a predetermined amount before the linkage begins bringing in the front carburetor.
As I continue opening the throttle, I begin bringing in the secondaries along with the front carburetor.
And eventually?
WFO. Eight barrels. Game on.
The graphic above makes the progression easy to see:
Light throttle → rear carburetor
More throttle → front carburetor begins opening
Wide-open throttle → both four-barrels available
That's progressive linkage.
You can.
That's where the difference between progressive linkage and 1:1 linkage comes in.
With a 1:1 linkage arrangement, both carburetors begin opening together rather than waiting for the second carburetor to be brought in progressively.
There are applications where that makes perfect sense.
But think about what happens on a street car with two four-barrel carburetors.
If both carburetors respond immediately every time you touch the accelerator, you're introducing a lot of throttle area very quickly. The engine can feel much more aggressive at small throttle movements.
Progressive linkage lets me drive the Impala primarily on the rear carburetor and progressively bring in the rest of the available carburetion as the engine needs it.
For my combination, the two biggest benefits are:
Drivability and fuel economy.
I'm not trying to feed the engine through eight barrels every time I pull away from a traffic light.
But when I put my foot into it, they're all there.
The easiest way to understand the difference is this:
One carburetor opens first.
Additional carburetors are brought in as throttle demand increases.
At wide-open throttle, all carburetors reach their required full-throttle position.
The carburetors begin opening together.
Throttle movement is applied to both carburetors rather than staging the additional carburetor later in the throttle travel.
Neither system is automatically correct for every multiple-carburetor engine.
The manifold design, carburetors, engine combination, vehicle weight, gearing and intended use all matter.
A street-driven cruiser and a competition engine aren't necessarily going to want the same throttle characteristics.
Dual quads aren't the only place you'll find progressive linkage.
Another classic example is the three-deuce, or 3x2, setup.
Instead of two four-barrel carburetors, a traditional three-deuce arrangement uses three two-barrel carburetors.
In a typical progressive arrangement, the center carburetor acts as the primary.
During idle, cruising and light-throttle driving, the engine operates primarily from that center carburetor.
As the throttle is opened farther, the progressive linkage begins bringing in the front and rear carburetors.
At wide-open throttle, all three carburetors are available.
So although a dual-quad and a three-deuce setup look completely different, the basic idea behind progressive linkage is the same:
Use the carburetion you need when you need it.
Then bring in the rest when you're asking the engine for more.
Yes—and this is an important part of setting up a multiple-carburetor system correctly.
Progressive linkage typically allows you to control when the additional carburetor begins coming into operation.
Bring it in earlier and the engine gets additional throttle area sooner.
Bring it in later and the engine spends more of its throttle travel operating primarily on the main carburetor.
The correct adjustment depends on the particular engine and carburetor combination.
Whatever linkage you're using, operation should be checked carefully with the engine off. Make sure the linkage moves freely, doesn't bind, returns completely to idle and allows the carburetors to reach the intended wide-open-throttle position.
Never assume that bolting the linkage on means it's adjusted correctly.
If you're building or changing a multiple-carburetor setup, there are complete linkage kits available rather than fabricating everything from scratch.
The important thing is matching the linkage to your specific carburetors, manifold orientation and intended method of operation.
For dual-quad combinations, Summit Racing carries progressive linkage components and kits from manufacturers including Edelbrock and Lokar.
Edelbrock complete Dual Quad Kit
Before ordering anything, verify carburetor model, mounting orientation, spacing and manifold application. Multiple-carb setups vary considerably, and a linkage kit that works on one intake may not work on another.
I wouldn't make the blanket statement that every street-driven multiple-carburetor engine should use progressive linkage.
There are too many different combinations for that.
What I can tell you is why I use it.
My Impala is a street-driven car. I want smooth throttle control when I'm cruising around, and I don't need both four-barrels responding every time I barely move my foot.
Progressive linkage gives me that control.
But it doesn't take anything away when I actually ask the engine for everything it has.
At wide-open throttle, I still have both four-barrels.
All eight barrels.
That's the beauty of progressive linkage.
You don't eliminate the additional carburetion.
You decide when it comes in.
Want to know why hot rodders run multiple carburetors in the first place?
That's a separate subject—and one we'll dig into next.
This article may contain affiliate links. If you purchase through one of these links, I may earn a commission at no additional cost to you.
Like our hands-on automotive content?
Add V-Twins to V-8s as a Preferred Source on Google.
Comments will be approved before showing up.
This site documents real builds, tools, and shop work from my own projects. Some pages are showcases. Some are how-tos and tool reviews. If you’re working on a project and want experienced guidance, I offer one-on-one coaching.