It was Mark Twain who once wrote: “The reports of my death are greatly exaggerated.”

The same could be said about the basic four-barrel carburetor.

We find ourselves well into the second decade of the 21st Century and, by now, everybody was supposed to be in flying cars—and yet the carburetor still flourishes. One major reason for this is simplicity but it doesn’t hurt when Edelbrock invests in what could be termed the next generation racing carburetor.

Despite its external similarities to that brand from Bowling Green, Kentucky, this is a straight from a clean computer screen creation. There are so many changes to the Edelbrock VRS-4150 over the basic square flange 4150 carburetor that this story will require significant length to detail so let’s get started. 

For anyone with even a rudimentary knowledge of carburetors, the ability to adjust the carb to meet the individual needs of the engine across a wide band of operation is the best way to build a universal carburetor. The VRS-4150 offers a ton of adjustability built into its design improvements, making this carburetor a source of joy for carb tuners everywhere. .

Carburetor size is always one of the first questions and the VRS-4150 is currently offered in three sizes: 650 cfm, 750 cfm, and 850 cfm, exclusively in a mechanical secondary configuration. The carburetor offers four-hole idle adjustment and, as we will detail in a moment four separate metering circuits as opposed to the more traditional two standard circuits in most other carburetors.

Edelbrock VRS-4150 carburetor
It’s hard to tell without a typical 4150 carb next to it, but the Edelbrock VRS-4150 is actually a half inch taller than most carburetors. The throttle linkage is drilled with configurations for the 700-R4 and 200-4R TV cable. Also note in the center of the throttle body is a separate idle air bypass adjuster, one for each side of the carburetor. (Image/Jeff Smith)

Exploring the Outside of the VRS-4150 Carburetor

Visually impressive, the VRS-4150 offers a single casting design that incorporates the throttle plate with the main body, so there’s no gasket or attaching screws. The main body is also a half inch taller than a typical 4150 which tends to help stabilize fuel delivery. The throttle plate also incorporates a multi-position flange that can accommodate either a 4150 or a 4500 style manifold pattern.

Keeping with the external features, the float bowls feature large, clear glass sights for setting float levels along with separate bowl drain plugs that are handy when changing jets. In addition, the bowls offer the ability to plumb fuel from either side. There are also both large and small vacuum ports extended from the front and rear of the throttle plate. The throttle linkage is also drilled for both 200-4R and 700-R4 TV cable linkage fittings as well as the kick-down linkage provisions for the TH350 transmissions.

close up of throttle side of a Edelbrock VRS-4150 carburetor
The passenger side of the Edelbrock carb features the dual feed connections which are the same effective length as a typical 4150 carburetor. There’s also the added feature of the bolt-on TPS provision (arrow). (Image/Jeff Smith)

Among the most useful additions to the Edelbrock VRS-4150 is the pair of idle bypass adjustment screws located on both sides of the main body. These adjustment screws offer the ability to set curb idle speed instead of using the throttle stop on the linkage. Idle bypass is especially important for competition and hot street engines with long-duration camshafts and very low idle vacuum numbers.

bottom view of a Edelbrock VRS-4150 carburetor
Turning the carb upside down allows us a view of both front and rear main vacuum port options as well as both ported and manifold vacuum connections toward the front of the carb for vacuum advance or potentially other vacuum-triggered devices. (Image/Jeff Smith)

By using the idle air bypass circuit to set idle speed separately, this allows the throttle blades to remain in their ideal position relative to the idle transfer slot. This bypass circuit eliminates the need to drill holes in the throttle blades to create sufficient inlet air into the engine when low idle vacuum requires a less restrictive inlet for idle speed.

Another nice feature is the built-in fixture on the passenger side of the throttle body for the addition of a throttle position sensor (TPS). This can be useful for either data logging to ensure wide-open-throttle (especially in road course of autocross applications), or it can also be used to establish TPS signals for electronic automatic transmissions like the 4L60E/4L80E.

Top view of Edelbrock VRS-4150 carburetor throat
This overhead shot reveals the annular discharge boosters used in the 750 and 850 cfm versions. The 650 cfm VRS carb will retain the more traditional down-leg boosters. You can instantly see the four circuit application by virtue of four separate air bleeds for each venturi. (Image/Jeff Smith)

A Look Inside the VRS-4150 Carburetor

With most of the exterior features covered, we can get into the heart of this carburetor and detail the four metering circuits. A typical 4150 and many 4500 carburetors use a two circuit system. One is for the idle side with the other for main metering. These carburetors can be identified by the two air bleeds normally found on the corner of each venturi in a typical 4150 carburetor.

Edelbrock VRS-4150 carburetor carburetor jet diagram
This Edelbrock illustration reveals the position of each of the four air bleeds for the separate circuits. The high speed bleed is the farthest inboard, followed by the low-speed bleed, the intermediate circuit bleed, and the idle air bleed in the farthest outboard position. (Image/Edelbrock)

By looking down through the top of the VRS-4150, you will instantly be greeted by four separate screw-in adjustable bleeds for each venturi on the carburetor. These are delineated from the outside toward the inside of each venturi as the idle/transfer slot, intermediate, low-speed main metering, and finally high–speed main metering circuits. Each of these circuits exercise control over a separate portion of the overall fuel delivery curve.

It’s really not as complex as it sounds.

close up of throttle blades on edelbrock VRS-4150 carburetor
The intermediate circuit introduces fuel through this small brass outlet located roughly in between the bottom of the annular boosters and the throttle blades. This circuit is used for additional fuel curve tuning separate from the main boosters. It can make part-throttle operation fall into an overly-rich condition however..   (Image/Jeff Smith)

The idle and transfer slot portion controls exactly what the description infers. The amount of fuel delivered is controlled by a small screw-in jet located in the main metering block. The air bleed located on the top of the carburetor controls the amount of air and is generally balanced in size with its corresponding fuel restrictor.

The intermediate circuit could be considered the more independent circuit of the four. The intermediate circuit was first added to older Holley Dominator carburetors and were assigned the term three-circuit carbs. Instead of supplying additional fuel through the boosters, the intermediate circuit employs a separate discharge tube that exits from the wall of the venturi roughly halfway between the booster and the throttle blades.

Metering block & jets for a Edelbrock VRS-4150 carburetor
An example of the VRS-4150’s sophistication can be found in the metering block. The callouts refer to each of the three separate circuits. The fourth being the intermediate circuit is controlled by a separate jet on the front side of the metering block. Arrow A reveals the idle feed restrictor that also controls the transfer slot fuel. Arrow B indicating the low-speed circuit, while arrow C references the high-speed circuit. With the power valve removed, you can also see that the power valve channel restrictors also use screw-in bleeds to make them easily adjustable. (Image/Jeff Smith)

The Edelbrock VRS carb uses an individual fuel jet located on the float bowl side of metering block for each venturi on the carburetor. This circuit tends to be more velocity sensitive.

As an example, if the entire fuel curve is slightly lean, increasing the intermediate circuit jet size will add more fuel at the top end of the rpm curve (let’s say from 5,000 to 7,000 rpm) as opposed to the entire curve including the bottom half from 3,000 to 5,000 rpm.

backside of a Edelbrock VRS-4150 carburetor metering block
The fuel bowl side of the metering block looks a little more traditional starting with the main jets, arrow A. There is also the addition of the intermediate circuit jet, arrow B, and finally a supplemental jet for idle and transition slot fuel that in this application is blocked off, arrow C. This jet is for competition engines with large camshafts that pull very little vacuum and need more fuel to feed the idle circuit. (Image/Jeff Smith)

Plus the original single main circuit has been expanded into two. This pair splits the fuel delivery curve into low-speed and high speed areas. These emulsion circuits operate more closely to a typical performance carburetor. So by changing bleeds in each circuit the carburetor can more accurately achieve the engine’s ideal air-fuel mixture curve.

The final circuit is the idle side that operates very similarly to all other idle circuits in terms of using an idle feed restrictor and an idle air bleed on the top of each venturi. So with an idle, low-speed main, high-speed main, and an intermediate circuit, we have our four circuit carburetor.

Edelbrock VRS-4150 carburetor metering block
This side shot of the metering block reveals a slightly better view the position of the main well bleeds for the low and high-speed sides of the two separate main circuits. The low-side circuit offers a pair of air bleeds while the high-speed side carries three bleeds for broader adjustability. (Image/Jeff Smith)

The beauty of this much circuitry is that very finite changes can be made to adjust the fuel curve. This of course, points this carburetor as intended mainly for serious competition use but also offers the veteran carburetor tuner the ability to make finite changes to the fuel curve over a broad rpm operating range. While these kinds of tuning options have been available in the past, they were the result of serious modifications by professional carburetor modifiers. Now much of that customization is available in an off-the-shelf performance carburetor.

inside float bowl of a Edelbrock VRS-4150 carburetor
This inside view of a secondary fuel bowl reveals cutouts in the float for secondary jet extensions. What may not be as easily seen is the slight increase in fuel capacity. (Image/Jeff Smith)

A design with this many improvements often also calls for unique parts, but the good news is that many standard 4150 replacement and tuning parts like main jets, bleeds, and power valves are completely interchangeable.

We may not yet be in the age bubble-top, cartoon Jetsons flying cars just yet but we have definitely arrived when it comes to 21st Century tunable carburetors. 

disassembled Edelbrock VRS-4150 carburetor on table
While the VRS-4150 is a complex carburetor from a tuning standpoint, mechanically it is really simple as shown in this exploded view. The design integrates the throttle plate with the main body of the carburetor—eliminating a gasket and several attaching screws. (Image/Jeff Smith)

Edelbrock VRS-4150 Carburetor Specs

Part NumberCFMVenturi Dia. Throttle Blade Dia.Booster
EDL-13077501.375″1.6875″Large Annular
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.