Carburetors have been feeding engines for decades, and the Holley brand has been there for most of that time. Holley started building carburetors back in 1903, but since we’ll only talking about four barrel carburetors for this story, we’ll pick up somewhere in the late ’50s.
There are many varieties of Holley carbs available for the power-hungry enthusiast.
The trusty 4150 series carburetor first appeared in 1957. Once the crazy ’60s hit full-swing, all bets were off, and the lowly four-barrel gave way to six and eight-barrel applications by simply multiplying the number of carburetors atop the intake. Today, those ultra-rare, multi-carbed applications spend more time under the hot lights of auction houses than they do on the highways of America, so again, we’ll stick with the bread and butter of barrel-dom, and focus on the core of performance carburetion: Holley’s 4150, 4160, and 4500-series carburetors.
Both 4150 and 4160 Holley carbs used basically the same body, although there could be differences like mechanical or vacuum secondaries or whether the carb has a choke mechanism or not.
If you’re scouring swap meets and foraging through boxes of fuel parts looking for that perfect carburetor for your application, you first need to know how big a unit you’ll need. That information flows at the speed of light over the internet, and those who need a link of motivation, Holley even has a carburetor selector guide on their website.
Every Holley carburetor has a list number. For carburetors with a choke assembly, the list number is the top number on the choke housing. The carburetor may or may not have the word "list" or an "L" before the number.
When looking at a swap meet carburetor, knowing what model you have in your hand is the first step, and that’s why it’s good to look at some foundational differences between each of these three series’ of carburetors that make up the lion’s share of sales for Holley.
If the carburetor doesn’t have a choke assembly, the list number will be clearly stamped on the side of the body.
4150 And 4160 Carbs
Both the 4150 and the 4160 series are square-bore carburetors, and both will fit on the same mounting area. The main difference between the two is that the 4150 uses metering blocks between both the primary and secondary fuel bowls, whereas the 4160 uses a metering block on the primary side, and a metering plate hidden inside the bowl on the secondary side.
The metering block has removable jets to help tune the fuel supply for each barrel, but the metering plate uses drilled orifices to meter fuel. To adjust fuel delivery in a plate, it must be replaced, or drilled to a larger size orifice. This is an area to check when buying a used carburetor, as the hole may have been drilled too large for your application, and the person that drilled the hole may not have documented their work.
Holley 4150 carburetors will have metering blocks on both sides of the carb body. This allows for easier tuning and adjustability.
The 4150 uses center-hung float bowls front and rear, while a 4160 uses side-hung floats. A 4160 series can be converted to a 4150 and vice-versa, but typically the upgrade to a 4150 would be the most common. Both series can be had in mechanical or vacuum secondary configuration. The vacuum secondary has only a primary power valve and accelerator pump, while the mechanical “double-pumpers” have accelerator pumps on both primary and secondary circuits. Some 4150s even have power valves on both circuits depending on the model.
Holley 4160 carburetors use a metering plate on the secondary circuit that has precisely-sized holes to meter the fuel feeding the rear of the carb. They are tunable, but to increase fuel, you need to replace the plate with one having larger holes on the bottom edge of the plate, or drill out the holes in the original plate. This plate has been drilled out and thankfully, whoever did it recorded the change.
The 4500 series carburetor stands out from the rest, and is easily recognizable due to its size. Starting out at 750 cfm and growing to double that size, the Dominator is definitely a high-performance carburetor. It was originally designed in the late-’60s for NASCAR, and of course enthusiasts wanted a streetable version. The Dominator is designed for serious performance engines, and requires their own intake mounting due to their much larger bores.
The Holley carburetor has evolved over the years, and in 2009, Holley introduced their Street Avenger line of carburetors. The 4150 design features billet metering blocks and base plate to help save weight, and also has vacuum secondaries and an electric choke.
All mechanical-secondary 4150 Holley carburetors will have two accelerator pumps, one on the bottom side of each fuel bowl. Likewise, the fuel bowls for 4150 units are different than those used on 4160 carburetors, and can be identified by having an individual fuel inlet to each fuel bowl.
The HP series carburetor is for racing or serious street performance, and doesn’t utilize a choke mechanism. They also have upgrades such as down-leg boosters and tunable air-bleeds for fine-tuning the fuel curve.
You should also consider the vacuum needs of the engine. Holley carburetors typically have a large vacuum port on the base plate for PCV operation, but also consider how many other ports you'll need. You may want intake vacuum or ported-vacuum for your distributor advance. Ported vacuum would be supplied via a port on the primary metering block where constant vacuum would be from any of the ports on the base plate.
You might also hear of a 4165 series, which is also a squarebore, mechanical-secondary double-pumper with metering blocks and accelerator pumps on both circuits. The 4175 is a spread-bore-style carburetor that was designed to replace the QuadraJet.
The 4010 series is a square bore that can be found in either mechanical or vacuum secondary configuration, and the 4011 is a spreadbore version of the 4010.
How Do You Tell?
Identifying Holley carburetors can go beyond looking for metering blocks or fuel feeds, and Holley helps by issuing list numbers. The list number is the carburetor’s part number, and you can find it either on the choke housing (if equipped with a choke assembly) or on the carburetor’s body.
You may or may not see the word list or the letter “L” with the number, but the list number is always the top number you’ll find in either place. The number below it is the date of manufacture. The list number will tell you how the carburetor left the factory, and in what size configuration. It is definitely powerful information to have, and should be the first place you look when looking at a used carburetor. When researching or ordering Holley’s “Renew Kit”, this number is what you will need to know.
We asked Holley’s Keith Jessee a few questions to find out what they typically see when the carburetors come back home to roost and get renewed. Here’s what Keith had to say.
Chevy Hardcore: Are the biggest carburetor issues typically caused by Father Time/Mother Nature or previous owners?
Keith Jessee: The biggest issues are typically caused by the previous owner allowing Father Time and Mother Nature to degrade their carburetor. Lack of maintenance is the number one thing that will turn a flawlessly-functioning carburetor into a nightmare. This is especially true when the carburetor is installed on a vehicle that isn’t driven very often. The ethanol in today’s blended fuels will wreak havoc on your carburetor if left unchecked. When the ethanol in the fuel draws in moisture from the air, it doesn’t only create a gunky, slimy, goo inside your carburetor, it also dries out your seals and diaphragms. In severe cases, that moisture can start to corrode the casting of the carburetor.
Evidence of corrosion and buildup on the bowl side of this block indicates that it likely has the same amount of crud inside the passageways within the block. Be sure to clean everything! The jets have been removed, but also note the omission of a power valve (the big circle just above the jet holes.
CHC: Will a typical rebuild kit be sufficient to bring back a carburetor’s performance most of the time?
KJ: If the hard (cast) parts are intact, a rebuild kit and a can of carburetor cleaner is all you really need to get most carburetors back in operating condition.
CHC: What areas would prevent this from being the case?
KJ: I have seen some extreme cases of neglect, where the castings have been exposed to some serious moisture and have corroded past the point of no return. Obviously, cracked or broken castings would have to be replaced, and that typically isn’t very cost effective.
A corroded power valve may indicate issues within the metering block. There are press-fit plugs on the top-side of the block that can be removed to clean the passageways, but they must be reinstalled to the same depth in the block for proper operation.
CHC: Are there steps that are necessary to assure a proper rebuild, but are often neglected?
KJ: It’s very common for people to neglect cleaning smaller areas like air bleeds, emulsion orifices, power valve channel restrictors, and the idle circuits that are cut into the baseplates. I recommend using a can of carburetor cleaner with a stiff bristle toothbrush and being as thorough as possible. Make sure that every orifice or hole in the carburetor has been cleaned and rinsed out. It’s also imperative that you use the correct gaskets when reassembling the carburetor. We have a full staff of knowledgeable guys on our tech line that can ensure you are buying the correct carburetor kit and/or gaskets.
CHC: When shopping for a Holley carburetor at swap meet, are there any reasons to not consider a partial carburetor? Are there parts that must be there and in working order for it to be considered? Are there parts that are less necessary or easily located?
KJ: I would hesitate to purchase any used carburetor that had the choke horn milled off. When that choke horn was cut off, the one number that could identify that carburetor was cut off with it. You might have found a high performance diamond in the rough, or a stripped main body from an old dump truck engine. If you do find a partial carburetor with a fairly common list number, you can find replacement parts such as metering blocks, fuel bowls, and base plates fairly easily.
If the carburetor is apart, check all of the threads in the carb body to be sure that they are not stripped. Also, a straight edge can help you determine if the sealing surfaces are straight, or at least repairable.
CHC: When should an enthusiast consider a used carburetor over a new offering, or vice-versa?
KJ: You’re always taking a chance on a swap meet carburetor. It might have that sought after 3310 or 4779 list number that everyone knows and loves, but you really have to do your homework to know if it also has the correct metering blocks and base plate that were designed for it. When you buy a new carburetor from us, that simply isn’t an issue. The only situation where I would seek out a used carburetor is if I were looking to do a numbers matching rebuild or some kind of period correct retro build. As cool as the new Gen 3 Dominators are, I will always have a soft spot for the early Dominator carburetors with the velocity stacks!
CHC: Is there any information that someone shopping for a used Holley carburetor should know before plunking down their cash?
KJ: The most common issue we see is our customers are often misinformed on the dynamics of a carburetor: how it works, how to size and tune it properly, etc., and that’s okay! Carburetors are a complex device, and we certainly don’t expect everyone to be a carburetor expert. That’s why we have a staff of full-time Technical Service Representatives available to field your questions.
From The Forums
How do you know if you’re getting a deal or someone else’s headache? We asked a few folks on the forums about what they are looking for when looking for a carburetor. Here’s what they had to say:
“I don’t bother with date codes, if the choke horn has 3310 stamped on it, and it has two metering blocks, costs $50 or less, I want it!” – Rtanner
“I used to buy them at swap meets when I lived in Denver. Most were in great shape and were cheap. Folks would say they couldn’t be tuned for altitude and would give up. Problem was, they messed them up by changing things. I would buy them and go to the Holley list manual and put them back to stock. I would throw them on my Camaro, make minor adjustments, and sell them for quadruple what I paid for them since I could prove they ran.” – 540Hotrod
Our guys talk carburetors upwards of 40 hours a week, and are there to help the customer. If you’re hesitant to give up your hard-earned cash because you have some unanswered questions about that carburetor you’ve been eyeing, just give us a call! (270) 781-9741.
CHC: If an enthusiast is wanting to return his numbers matching carburetor back to its former glory, what is their best option?
KJ: We still do carburetor restorations on a case-by-case basis. In this case, you would call our tech line and tell them you would like to have your carburetor restored. At that point, we will work up an order and give you a Holley Custom Shop tracking number to identify your specific carburetor. Upon its arrival, we do a thorough inspection and take a “before” picture. Then your carburetor is replated, recolored, repaired (if needed), and rebuilt. We put your carburetor on the flow stand and set it to original factory settings (as we do with every carburetor that leaves the plant). We then take an “after” picture and ship it back to you.
CHC: Are there any specific benefits that someone utilizing Holley’s restoration services would receive?
KJ: When we restore carburetors, it is important to us that we return it to 100-percent original, right down to having the correct hardware holding it together. We devote a considerable amount of resources to tracking down the correct screws, linkages, levers, and so on to ensure the originality of the carburetor.
While complex in their circuitry, carburetors are not beyond the common enthusiast’s understanding. If you are looking for a carburetor for your application, there are plenty of options for you. Whether the box they came out of is brand new or dusty and dog-eared and found at a swap meet, Holley carbureotors are still a reliable way to make power.