The Stovebolt Site Forums The Shop Area Engine Shop What carbs are best?

Well I asked in the Greasy Spoon- to no avail. What carbs would be best for a dual carb setup(Tattersfield intake and Fenton headers with heater) on a 235? I have lots of good rochesters, but is there better available?

I've been reading up quite a bit on dual setups and there seems to be a consensus (if you can call CARBKING a consensus ) emerging that a pair of Carter W-1 carbs work nicely?

I bought a pair of both just to be sure...

I have a Tattersfield manifold also. I'm using a pair of Stromberg BXOV-2's.

The Carter W-1's are probably the best inexpensive units available. These have a leather accelerator pump, and a manual power system. Work well in a multicarburetor environment.

The Stromberg B series, and the Zenith 228 series may be slightly superior to the W-1 in design, but there are very few places on earth that have many parts; although there seems to be lots in a small hillbilly town in south central Missouri. The externally adjustable main jet makes for ease of adjusting the "cruise" mixture, and replaceable idle jets allow for easy (albeit expensive) modification to the idle circuit.

The Carter YF is an excellent design, and some were designed to run in a multicarburetor environment (twin-H Hudson units); but have a diaphragm type accelerator pump, which may be troublesome for enthusiasts that do not start their vehicle weekly and are forced to use :mad: ethanol.

The Holley 1904/1920 carbs with the glass fuel bowl have a low profile, and have a following of some who enjoy gimmicks (you can watch the float operate, and fuel enter the carburetor), but also have the diaphragm accelerator pump plus a diaphragm style power accuator. They also leak worse than a Rochester B.

And that brings us to the Rochester B. Since I was taught as a child to attempt to say only good, I will mention here only that the carburetor exists.

The above comments are the opinion of the poster, and since political season is growing ever closer, the poster approves of the post.

Others may have other opinions.

Jon.

Jon has even more good to say about the rochester b than I do.

You might consider Holley Weber 2bbl...with the proper adapter they're a great alternative. Another good alternative is Carter YF 3211S...which were original equipment on '61 235s, they don't leak, have electric choke and are great performers. I wholeheartedly support all the negative things you can say about Rochester Bs...I lke other suffered with them.

My experience with single or dual carbs is finding carbs that are not distroyed old junk and finding a pair, well is another story. So, I really like the Stromberg BXOV-2s, but like other old car stuff it may take a few to make one good one. Easy fix is to go with Langdon's NEW Holley-Webbers, gee, new stuff you don't have to re-invent. Granted they are ugly and don't look like 50s stuff, but they work really well.

Carbking,take a ride over to my place,you can see two of my trucks have Holley 1904's that don't leak,and have never leaked.No glass float bowl,so nothing to watch Since Holley 1904's where used by the millions on Fords,IHC's and even some GMC's,I think one should blame any fuel leaks on the mechanic and not the carb.
One thing to keep in mind,any multiple carb setup where all the carbs open at the same time,it would be nice to have matching airbleed and power valve restrictions.Even the dreaded Rochester b was made with many different specs.

Tony - obviously, you have NEVER put any gasoline in the gas tank, therefore the carbs cannot leak! :p

The early Holley 1904/1920 (1952~1961) used a glass bowl (more rigid than metal). This was discontinued in about 1962 due to breakage from clumsy mechanics, and the commercial rebuilders started replacing all of the glass bowls with the zinc alloy version. The Holley 1904/1920 suffers from one of same maladies of the Rochester B (insufficient screws attaching the bowl to the body). Over time, the castings warp, and leaks occur. But glad you are happy with your Holleys, just don't take them for granted. The glass bowls are less prone to leaks than the metal ones, as the glass won't warp, but the metal body still does.

And you are absolutely correct concerning matching carburetors. This is a area where many don't understand that specifying the type of carburetor does NOT specify the internal size or calibrations.

Jon.

Jon,glad we can agree,lol.I use the 1904 Holley's to replace Rochesters cause they are inexpensive and readily available,and are a worthwhile improvement.The other carbs you mentioned may be better,but they are much more costly.I use the metal float covers,just don't trust a glass bowl sitting over an exhaust manifold.The later 1920 Holley's used on non emissions Mopar slant 6's are a one piece design,cheap and easy to find,but need the idle restriction drilled out slightly(.001)to eliminate an off idle soft spot when used on a 235/261.The end result is a smoother running engine,more power and improved fuel mileage.Of course ya need to rework the air cleaner throat to fit on the Holley.
I'm not that familar with the old Strombergs,but I believe their strong point is the easily changed idle and air bleed jets,that's if you have a supply of jets or can make em.
It's been my experience,that the single bbl carbs originally intended for trucks have much larger power valve restrictions that car carbs.So dual car carbs will generally work better ,as in not over enrichening the mixture at wide open throttle.
But like we said,finding matched carbs can be difficult unless a guy wants to spend lots of time with pin drills,soldering up restriction jets and road testing different combinations.But actually,you'll never know if an engine is running to full potential without dyno or road tests when doing carb swaps.

Thanks for all of the input gentlemen, BUT, I think this is one of those times when one realizes that 'the more you know, the more you realize you don't know ANYTHING'.

I have a few GMC engines (248s and 270s) here with the Zenith carb on them. Is this what I am looking for?

Oly - the O.E. carburetors use on the 248 and 270 GMC are going to have too large a main venturi (unless you are building a high RPM, race only engine).

The information below is copied from a page on our website, and MAY either answer some of your questions (or cause more):

CARBURETOR SELECTION

When choosing a carburetor for your car, a little homework will often pay large dividends. Consider the following questions:

Is your car a 'numbers matching show car'?
If yes, you are generally restricted to the original carburetor or a duplicate thereof.

2. If no, is your car going to be used for sanctioned racing?

If yes, check with the sanctioning body for their regulations.

If no, is your car going to be based on some factory engine (Example. You have a 1966 Pontiac catalina with a regular fuel 389 and two barrel carburetor. You want more horsepower. Consider upgrading THE ENTIRE ENGINE to 1966 Pontiac catalina premium fuel 4 barrel carburetor specifications, or further to GTO specifications.) By duplicating a factory engine, the engineering has been done for you by the factory. YOU KNOW THE THING WILL WORK!

Assuming you answered no to all of the above, you MUST accept responsibility for doing your own engineering, and the following set of questions are designed to help you make your choice. Please remember that any choice you make will be a compromise. You may choose to maximize horsepower, drivability, fuel economy, changability, appearance or initial cost. Maximizing one category will result in reductions in one or more of the other categories.

Is it legal? The Federal Clean Air Act of 1966 took effect with the 1968 model cars. The Federal Clean Air Act applies to all vehicles licensed in all 50 of the United States. Additionally, some states may have emission requirements more stringent than the Federal level, but the Federal level is the minimum in all 50 states. (1998 addition). It is being reported in many publications that California vehicles through the year 1974 are now exempt from smog emission due to California S.B. 42. THIS IS INCORRECT! Remember government 101 (the state cannot override the federal government). SB42 reduced California's more stringent requirements on 1968 to 1974 vehicles back to the Federal level, and removed emissions on 1966 and 1967 California vehicles.

B. Do you want to use a single carburetor or some form of multiple carburetion?

If you wish to use a single carburetor, the following equation can be used for multi-cylinder 4-stroke engines: CFM = (RPM x CID) / 3456. This equation is familiar to most enthusiasts, but understanding the equation seems to be a different story. Most apply the equation for WOT (wide open throttle) to determine the maximum size of the carburetor, which is good, but only half of the story (unless you plan to drive on the street constantly at WOT). For street use, it is also important to use the equation for your normal cruising RPM, and these that CFM figure for the primary side of your 4 barrel carburetor. This will maximize the air velocity (and the primary efficiency) for your cruising RPM. Remember that too large a venturi means too small air velocity, which means a LEAN condition! We have found that, for modern 8 cylinders of 300 CID or larger, almost without exception, a spread-bore carburetor (small primary, and large variable secondary) will perform best on the street. We have a small quantity of high performance Carter spread-bore aftermarket carburetors (with electric choke). These are part number 9800 and are rated 800 CFM (200 primary plus a variable secondary). Also, consider whether the engine is a large displacement high torque, low RPM; or a smaller displacement high RPM engine; and also the breathing capability of the engine. Chevrolet found the small block to like smaller primary and larger secondary. The 1963 Corvette 327/350 used a 575 (225P/350S) CFM unit. Pontiac found the spread-bore 750 did not do as well on a 455 as an 800 (200P/600S). Chrysler used spreadbore 850 (250P/600S) on their 440 engine.

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)

MULTIPLE CARBURETOR SET-UPS

Assembling a multiple carburetor street set-up can be a tricky situation. Unless you wish to maximize appearance only, FOR BEST RESULTS, the number of carburetors should be a factor of the number of cylinders ie 2, 4, or 8 carburetors on an 8 cylinder, 3 or 6 carburetors on a 6 cylinder. (Four cylinder engines present their own set of problems - CALL). Before all you Chrysler 6-pack and Pontiac tri-power gearheads get your hackles up, please read further! I have tri-power on my own 1964 GTO because Pontiac put it there to maximize appearance, but a properly selected 4 barrel runs better! I didn't say tri-power won't work. It just doesn't work as well as a 4 barrel. When more than one source (carburetor) feeds a cylinder, turbulence exists at the point of join. This turbulence will cause the air fuel mixture delivered to the cylinders to break down at higher RPM. Please note that when the factorys used three two barrel units, they were primarily installed on relatively low RPM undersquare engines. Please also note that Chrysler used dual quads on their race engines with multiple carburetors, as did Pontiac with their Super Duty race engines.

Once you have determined configuration, you must choose carburetors. FOR BEST RESULTS, use:

(A) original carburetors from a similar multi-carb unit
(B) aftermarket carburetors whose manufacturer offers calibration pieces
(C) carburetors with mechanical power systems (especially important if building older units such as 2 x 2 on a flat-head Ford, etc.)
Your carburetors will probably have to be re-calibrated. Having a ready source of calibration pieces is useful. Modern carburetors utilize vacuum to determine auxilliary fuel flow (power valves, metering rods, etc.) A higher lift camshaft will lower the engine vacuum and require recalibration of the carburetor's power system. Many problems on street systems are a direct result of ignoring the vacuum signal, even when the proper size and type of carburetor are used.

Sizing carburetors for multiple units can be very tricky. Remember that two barrel carbs and four barrel carbs are rated with a different scale. Also remember that carburetors too large for your engine will run lean!

Linkage can be another problem. We recommend street dual quad systems run simultaneous linkage. That is, the throttle controls both carburetors as though there were only one. We suggest using the choke and idle circuits on both carburetors. This may mean fabricating your linkage.

Jon.

Something that posts on this thread point out is: THERE IS NO ONE PERFECT ANSWER!

One can maximize appearance, horsepower, economy, reliability, or cost in the set-up; BUT RARELY MORE THAN TWO OF THESE QUALITIES!!!

Each individual will set their own critera as to which issues are important to them.

Jon.

I replaced the Rochester 1bbl on my 235 with a Holley/Webber 2 barrel. I really cannot believe the improvement in driveability, power and economy. I just towed a u-haul trailer 400 miles in it and even with the bed loaded up, still got 17.3 mpg. I came back the same 400 miles, averaging 60 to 65 mph and empty, got 18.4 mpg in a strong crosswind.

This is compared to only 13 mpg with the vastly inferior Rochester.

hot rod dad.where did you buy your holley weber?

If you go with Langdons Holley/Webers I stronly recomend one of those:

[img]http://img136.imageshack.us/img136/2774/scoop49td.jpg[/img]

This is a combined fuel filter/pressure regulator.

This is a combined fuel filter/pressure regulator.
It´s Malpassi's "Filter King" which he designed for the original "Iso Rivolta" when he was Chief Engineer at Dell'Orto, because they had problems with to much pressure and pulsing from the mechanical pumps at high rpms in the italian sport cars.

The Weber carbs where flooding into the ventury if they got more the 3.5 psi.

Since I have it there is no more flooding, leaking and no mor neadle valve and seat trouble.

Frank

Where did you find your Holley/Webber Hot Rod Dad? I've been looking into replacing my Rochester 1bbl on my 250 with something better. Or would the Carter YF be a better option since I am looking into this just to increase my gas mileage b/c 11 mpg doesn't please my mom(who pays for my gas ). What modifications have to be made to my truck to get either of these to work(adapters or converting my manual choke)?

Thanks

Drew

P.S. What kind of gas mileage can I expect to get?

--------------------
'66 C-10 stepside

Tom Langdon sells them Holley Webers for $65.
Stovebolt Engine Co

I did a lot of carb and intake testing on a 261 Chevy engine a few years ago,wrote an article in Inliner's on the test.
The CFM charts are pretty accurate for street engines.My engine was moderately tuned,3/4 cam,Fenton's,more compression,always used heated intakes,a Offy 2 carb and then a Clifford single 4 bbl intake.The carbs were 2 Rochesters,2 Holley-Webers and a variety of single four and two barrels on the Clifford,Holley 390 4 bbl,Holley 500 cfm 2 bbl,a rare Holley 500 cfm staged 2 bbl,Carter 400 cfm 4 bbl,Edelbrock 500 cfm 4bbl,Carter WCFB and a Rochester 4GC.
All the carbs were tuned for use on my engine,some requiring internal changes to run their best.
I measured acceleration in second gear of a 3 spd from 2000 to 4500 rpm,measured the time it took and measured time between two road markers.And also took in how the carb "felt" ,like part throttle response and fuel mileage.
After all this testing,the 261 didn't need more than 350-400 cfm to run it's best.Both single and multible carbs performed the same one sorted out.The best response and power in my testing came from a single Holley 2305 500 cfm staged two barrel mounted on a Clifford intake.The Holley Webers worked just fine,but gave no more power than two stock jetted matching Rochester B's,the larger size from mid 50's Chevy cars.
The Holley Webers are good for relatively cheap money they cost,but they are ugly as hell.
I didn't get into Carter YF's or Strombergs cause in my opinion they are far too expensive.Same for Quadra-jets,good one cost 400 bucks.But thery both will work well id money is no object ot you get the carbs on the cheap.
For a simple test to judge your carb needs,hook up a vacuum gauge.Then using a lower gear,like second,apply full throttle and watch the guage,if your engine can tolerate more carb,the guage will go to nearly zero when ya first floor the throttle,then rise up to above 4 inches or so of vacuum as the rpm's near redline.

Any information about jetting the Holley Webers on a warmed up 261?

Since the jets are not aviable here in Germany, I have to orde them in the US. So I wonna hit the right spot with the first order.

Thanks, Frank

Hey guys just wondering about the Rochester b's. I am adding a dual setup to my 235. I already have two B's plus the original B on now. What are everyones problem with the B's? I would like to know if I should switch now before I go ahead and install everything.

I've run both single and dual Rochester's on a 235 with overdrive getting near 20 mph. They seem OK to me but then again I've never run anything else. As far as leaks go I ride an old Harley so I wouldn't notice something like that.

I am putting a 261 in soon (this weekend I hope) and have given some thought to switching to a pair of Rochesters from a 216 instead of the ones from a 235. I already milled the bases to fit my manifold. Any thoughts?

Stovebold,the stock main jets should work ok.The lowspeed or idle jet may need to be bumped up one size if the engine has a soft spot off idle.
I believe the carbs use Webber jets,you should have those in Europe?

Thanks Tony but what sizes are the stock jets?
I assembled my two W/H carbs from a lot of 5 1/2 used carbs that all came with different sizes.

Thank`s Frank

I don't remember the stock main jet size,whatever you have on hand,use the same size jet in both carbs and go from there.

If using a pair of late 40's Carter W-1's on an Offenhauser, where can one buy a linkage for the two?
Or is there a diagram from someone who has customed their own?
thanks

Rattletrap 52, Patrick's (ads all over Hemmings) sells an Offy linkage kit for two carbs. I think Chevs of 40s also stocks it, inexpensive too.

On my H/Ws, I ended up using .078"/195 metric (550 flow rating) in the secondary side. This is up from the .074" that came with carbs.

I have a few questions:

If I use the Holley Weber from Langdon's on my 1957 235...what is the process to deal with converting from manual choke to auto choke?

I have a Stromberg BXOV-2 carb and am also considering using it on my 235... Is this a good match?

A 2x1 intake with a pair of the correct Stromberg BXOV-2's would be a super match with split exhaust. With or without other mod's.
I say correct Stromberg's because the BXOV-2's came in many different sizes and jetting's.