The Stovebolt Site Forums The Shop Area Engine Shop Carter 4 Barrels; any good?

Hi Guys --
I'm more curious here than serious, but I noticed a number of Carter carbs on Ebay. Some are 500 cfm. They can be had pretty cheap, and that would be about right for a built 250 inline. (Most real hot factory V8s run around 1.8 cfm per cubic inch, and I've seen 283s work good with up to 750 cfm carbs, so 2 cfm per cubic inch is alot, but not to much with the right cam, porting,valves, et.)

Anyway, my only personal experience with Carter carbs comes from a couple of big pontiac motors a good many moons ago. So, do any of you have any personal experience running these 4 barrels on an inline?

Thanks,
Bob

If the Carter carbs are AFB design, then I think they're pretty good. I'm gonna run a 625 cfm Carter on my 292. I got it real cheap (it was a vendor return that came back cuz the choke wire was off.)

I run Edelbrock AFB carbs on almost all of my cars with "twin 4s" because I like the "set 'em and forget 'em" feature. That is, they don't seem to require the constand maintenance that some other carb brands do.

All in all, I really like 'em.

An AFB would be a lot of carburetor for an inline six, unless it was an awfully big one! While the total CFM might be OK at full throttle, high RPM, what about low speed and midrange performance? Too much venturi area results in very low venturi velocity and little, if any fuel flow through the high speed system. The result is a bad flat spot right off idle, or even a stall when the throttle is opened. If you can manage to get it up to high RPM, and stay there, it might be possible to jet it rich enough to run right. Forget getting away from a stop sign, though!

A 350 cubic inch V-8 at 6,000 RPM flows 608 CFM, and that's figuring it at 100% volumetric efficiency. Realistic VE is more like 92% on the average street engine, so that brings the effective CFM down to 560!

A 250 engine at 8,000 RPM only flows 578 CFM, so you'd better build that bottom end pretty bulletproof!
Jerry

What I like about AFBs is the secondary air door. It's sorta like an "on-demand" limiter. When you're running on the primaries, you only have a maximum air flow of half (or a little less) than the rated CFM capacity. Then when WOT is reached and the secondaries kick in, the air door limits the amount of air to that which is demanded by the motor.

It's a little different from a mechanical secondary setup on say, a Holly double pumper. There the secondary butterflies open and you got the full capacity of the carb wide open. But the AFB (and the Quadrajet) limit the amount of airflow, so that it doesn't overwhelm the motor. That's why some factory Q-jet motors (L69 305 for example) have a carb that's rated at a maximum cfm of 695...which would normally be WAY too much for a 305. But by limiting the secondaries, that carb works fine (well, as fine as a q-jet can) with a small motor.

I'll letcha know how the 625 Carter works out on my 292. We're gettin closer and closer. I just got the headers painted with high-temp stuff and as soon as I can get my El Camino functional, I'll dig into the truck.

I ran a Carter AFB on a slightly warmed-over 283 about 35 years ago, and it ran OK, but the fuel mileage was lousy. The original jetting was for a Pontiac 389, and we had to jet it considerably richer to get good midrange throttle response. The Q-jet has a definite advantage on small-displacement engines, because it has a 3-step venturi, and doesn't require a lot of volume to get the high speed system working. I put a Q-jet for a 455 Buick on a 440 Dodge tractor-pull engine once, and got 714 HP at 6,500 RPM out of that one. With the .060" overbore, the 440 had a total displacement of 456 cubic inches, and the 455 jetting was just right.
Jerry

We ran a Carter 400 CFM AFB on a Ffoorrdd 300 CID with standard transmission for many years and several hundred thousand miles. Worked well. I wouldn't like to use a larger one on a street engine though.

If we were going to do it again, would use a spread-bore (Rochester Q-Jet or Carter TQ) because of the small primary side.

Jon.

Two Holley/Weber 5200s add up to 400 cfm if measured as one 4 barrel. I think the 400 cfm mentioned by carbKing probably is about right. It's 1.6 cfm per inch. I have two webers and a bucket of parts. I just don't know if I want to fool with dual carbs. The single holley/weber 2 barrel I am using now works great, but this is a very tired stock motor. Eventualy I'll break free of the paralysis of analysis and make a decision!
Bob

Pontiac had an optional Rochester Q-Jet on the OHC-6 250 CID. Don't know if the manifold would fit or not. Carb should be just perfect for a warmed up 250 Chevy.

Jon.

I've got the Edelbrock 600 cfm 4 bbl carb on my 350 and I LIKE it!

Don't Edelbrock and Carter have something to do with each other??

Hey Carbking: What year Pontiac was that? I might do a bit of hunting the yards.....

The warmed up 261 in my 37 has seen a number of manifold and carb set ups in the past 6 years,a 250 engine certainly has better breathing, but ya can draw a few conclusions from my actual experience.
I started with two Rochester B's on a heated Offy 2 carb manifold.The B's were the larger mid 50's models,stock except the power valve jet was reduced in size by .008 of an inch.The B's ran excellent, but leaked fuel out of the accelerator pump linkage passage in the carb on hard acceleration.Then I got 2 rebuilt Holley Webers with adapters from Stovebolt Engine Co.The Holley Webers carbureted very nicely,smooth power no bogging even when flooring the pedal at relatively low speeds.But the H/W carbs suffered from quality control problems,erratic idle,intermitent hot start flooding problems. Seems the carbs were bead blasted by the rebuilder,constant tiny pieces of grit clogged passages despite repeated disassembly and cleanings.
I then got a Clifford 4 bbl heated intake, borrowed a new 500 cfm Edelbrock from a friend. The carb was too rich during light throttle right out of the box, a change of jets and rods got it running nicely.Very responsive on the primaries but always bogged when opening the secondaries.The Edelbrock has a weight controlled secondary air valve like a Carter AFB,I got the heaviest weight ,messed with secondary jetting, but never cleared the bog.My friend needed his carb back, I then found a nice 500 cfm Carter AFB, same story as the Edelbrock.Next was a 400 CFM Cater AFB, unfortunately this particular model didn't have a secondary air flap,the same bog situation when using wide open throttle at lower speeds.I looked for a 9400 series Carter,$400 bucks, too much for me.
From then on I ran a variety Of Holleys,including a 500 cfm 2 barrel(which is actually 370 cfm when rated like a 4 bbl.Despite everyone telling me the 2 large throttles would kill response, I got the carb to function excellent by swapping out the metering block for one with smaller idle restrictions and reduced power valve channel restrictions.I could floor the pedal at 2000 rpm in high gear without a hesitation and it delivered the same fuel mileage as the other carbs.At one point I even tried a Holley 600 cfm 4 bbl for kicks.It worked quite well once a heavy spring was used to limit the opening of the vacuum controlled secondaries.
I was gonna try a Q-jet, but good ones are too darn expensive for my tastes, but it will probably work ok on a 250-292 engine. The 261 doesn't need more than 350-400 cfm for street use.I have a Holley 390 cfm 4 bbl on it now,runs great.
One time I took a ride in a car. when the guy floored the pedal, the engine bogged, then cleared and took off.The driver was impressed with the power,"feel that pull" he said.His car would have been faster with a smooth opening secondaries but the normal acceleration after the hesitation made it seem faster to him.
Tony

Pal - Pontiac had the Q-Jet option on the 230 in 1966 - 67; and the 250 in 1968 - 69. The 1966 carb would be the least desirable.

Truckedup - The problem with secondary bog with the Carte AFB generally lies with the air valve, as you guessed; however, weight (mass) of the valve is not the only variable. The angle of the airvalve on the aftermarket AFB's is designed for oversquare (high RPM) engines. Changing the valves to those from a high torque low RPM engine (ie. early 60's Pontiac) will generally clear the bog, assuming the carburetor is properly sized to the engine.

The following information is copied from our website:

"To help you pick the size carburetor for street use, consider the following Carter aftermarket carburetor sizes:

Square-bore (secondary is variable, based on engine demand)

400 CFM – 200 (P), 200 (S)

500 CFM – 225 (P), 275 (S)

600 CFM – 250 (P), 375 (S) (this is NOT a misprint)

625 CFM – 250 (P), 375 (S)

750 CFM – 375 (P), 375 (S)

950 CFM – 375 (P), 575 (S)

Spread-bore (secondary is variable, based on engine demand)

800 CFM – 200 (P), 600 (S)

850 CFM – 250 (P), 600 (S)

1000 CFM – 400 (P), 600 (S)"

Jon.

That's why I prefer Holley vacuum secondary 4 bbls, it's very simple to tailor the secondary opening point and the rate of opening by changing the vacuum chamber spring. And with a $10 quick change kit,it takes about 2 minutes without removing the carb or fussing with more than 2 screws.

Both the Carters and the Holleys have their advantages and disadvantages. One of Holleys big advantages is the availability of parts, such as the kit you mention.

On the other hand, one of the Carters big advantages is total control of the primary fuel circuit (via metering rods and springs) without opening the carburetor.

Jon.

Okay, this is getting to be a very educational thread!
Now here is a different angle.

This carb on ebay ( web page ) is an autolite off an earlier 289. Were these Holley 500 carbs?
Doesn't it flow at around 350 if measured like a 4 barrel?
Would it be a good choice for a 250 with mild cam, ported, 1.6 exhaust valves, and a few other goodies?
Bob

I initially started this thread because I am not sure what carb I want to use after I rebuild my 250. The Holley/Weber I am using works great and if I was keeping my engine stock I would not dream of changing. But, I am going to clean up the ports, put in 1.6 exh valves, and upgrade to a cam that is 194/204 duration @ .050. The Weber only flows at 200cfm if measured like a 4 barrel, and I really think that getting the full benefit of the lumpier cam, cleaned up ports, and bigger exhaust valves, will take a bigger carb.

I am very interested in the carter 2 barrel that came on some 258 sixes in Gremlins, but I have not been able to find specs on it.

I would love to have a Holley 390, but they're a bit to rich for my blood. After reading all the posts from you guys I really think I need something between 350 and 400 cfm, but what? I don't really want to fool with dual carbs.
Bob

The Autolite 2100 is a Foorrdd designed Holley built 2 barrel. While almost bullet-proof (and unlike other Holleys, they don't leak!!!), we will never again migrate one from one application to another; due to a total lack of literature and tuning parts. This is really an excellent carburetor. Too bad that Autolite was a "captive" Foorrdd company, and retail literature was not printed.

As far as the Carter 2-barrels are concerned, the BBD is VERY difficult to modify. The WGD will accept AFB jets and vacuum piston springs, so some tuning parts are available. The WGD is also a superior design, and much more reliable than the BBD series. The older (40's and 50's) WCD series are much easier to modify.

As to CFM, you pretty much have to guess. As these were O.E. applications only, Carter had no reason to publish CFM ratings, and didn't.

Carter did make a very few WGD aftermarket carbs (55 Chevy and VW bugspray to name a couple), but parts for these are different than for the O.E. WGD (read rare and expensive).

Jon.

I think one of those 2 barrels off an AMC 258 might work really good. I had a 258 in a Pacer, but it had a 1 barrel carb of some sort. I think the 2 barrels were a hi pro option. They show up on ebay quite often and are pretty cheap. Maybe I'll just buy one and give it a shot! Then again the same can be said of the Autolite. They are plentiful and cheap, so here i go again; the paralysis of analysis.
Bob

Carbking, Holley 2300's and 4150's leak if butchered by ham fisted mechanics.You certainly have a large shop and way more experience than I do, but I rebuild and sell about 50 Holley modular carbs a year and never had complaints about leaking fuel.I buy carb cores on Ebay and at local swap meets, 90 percent of those carbs have jetting that's been changed way off specification ,and improperly adjusted floats.Since these type Holleys are the most popular for performance use,have external adjustable floats and readily available jets and such,many well meaning tuners feel that's a license to turn every screw and re jet a perfectly good carburetor.Guys reef down on the bowl screws until the main body warps trying to stop leaks from improperly installed gaskets, wrench power valves until they rupture,drill out air bleeds, then blame the carb.It's just amazing the damage they do.I mill the main body true again,put in Holley brand parts, return the carb to stock specs ,good as new.
Holley's, just like AfB's or for that matter most any carb, will work great out of the box if used for an engine close to the original application it's designed for.
The Holley 2300 I mounted on a modified stock intake on a 261 cube Chevy 6 cylinder carburetes excellent, an amazing up grade from the stock 1bbl Rochester,all that for a $19 Holley kit and a 10 buck swap meet carb core.The Holley is originally off a 266 cube IHC V-8, flows about 220 CFM as rated like a 4bbl.
I really like AFB's but when using the carbs off spec like on my modifified 6 cylinder,it required a lot of tuning with parts I couldn't easily find for reasonable money.
Carbs are just like women,treat em nice,it's wonderful,treat em crude,it's hell

Can anyone identify this carb. web page The little bit of base I can see looks like it would bolt right up to the Stovebolt adapter I am using. But that would be pointless unless it flows at least 300cfm measured like a 4 barrel.
Bob