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I'm gathering parts for the rebuild on a 1960 235. While I admit to being a "Mouth Breather" as Jerry likes to say, I have always wanted to have a dual carb setup on an inline 6. I have read most everything on the BOLT dealing with this, there are quite a few folks using these and making them work. All this being said I am open to recommendations on manifold and carb choices. There are several Vintage manifolds available , for a price, and many being repopped. Just asking for thoughts and advice prior to spending the money. Thanks.

There is iron in Jerry's words.
However, the key to making it work is to have two identical and much smaller CFM carburetors than stock, and the ability to synchronize them.
If I were to ever begin to breathe primarily though the mouth and insisted on using dual carbs, I would first make sure to install a T5 and the appropriate rear axle gears in order to keep the engine very near the optimal operational RPM for a Stovebolt engine in all 5 gears so that when you shift and step on the go pedal, the engine actually goes right away. That is the beauty of what the T5 with appropriate gearing does for a Stovebolt engine even without any other modifications.

There are a couple of ways to go at this.

New intakes, I would go with the Clifford dual 2X2 intake with integral water heat. He sells them with Weber 38/38 carbs but he will also sell just the intake and a pair of carb plates. Skip the Weber 38s. Consider a pair of 1974 Ford pinto Holley Weber 5200 carbs. These are small progressive two bbls. They work really well. That, and the intake is already set up for hot water heat.

I run that intake but I run it with a pair of 2300 Holley two bbls on a very modified 261 motor.

New and Used 2x1, really any will work. I prefer Weiand 2x1 intakes because they use a pair of tabs and a cross rod on the intake itself which makes sorting out linkage easier. For single bbl. Stay away from the Rochesters. Too big and troublesome.

Smaller carter carbs would be better, like w-1. But you can also use a couple of adapters and run the pinto carbs which I think is a better choice.

Offy manifolds, another good choice. But buy the intake directly from offy. They have a new owner, young guy, rebuilt all the tooling and equipment, casts and machines everything in the USA. Excellent customer service. Most times you call you get the owner. Anything fro speedway or other places other then direct from offy, offshore stuff made under an old license arrangement. Skip that and get the real thing.

One issue with the offy manifolds (dual and triple), if you want to run hot water to the cast in heat chamber, you have to weld up the sheet metal core plugs that are staked in the bottom of the manifold or else the water will leak.

Now, let’s talk about mouth breathing. The detractors are wrong. Adding a second carb will add power. A little power. Why, because these are little motors and they are really in essence tractor motors. So the improvement is going to be relative. So there is a limit to what kind of additional power you can drag out of them. But here is the thing, the 235 and 261 responds to hot rodding just like any other motor. The problem, if you are thinking you are going to get a lot of power after modifying things, you are going to be disappointed.

On the other hand, if you like to tinker, you will love tinkering with a dual carb set up.

I'm pretty firmly convinced that the time, effort, frustration, and expense incurred by a swap to dual carbs on an inline six just isn't worth the effort. That being said, some folks just have to whiz on an electric fence before they can be convinced it's not really a good thing to do. The 290-something cubic inch 261 that's on the drawing board right now will most likely run a single carb, but it's either going to be a Rochester 2G, or maybe a Bendix/Stromberg 2 barrel designed for a small displacement MOPAR V8 like a 273 or a 318. That's going to require some creative whittling and welding on a 1 barrel stovebolt intake manifold. No matter what's done to "improve" intake and exhaust flow is going the be offset by the horrible flow characteristics of the cylinder head. Connecting two heavy chains with a paper clip doesn't accomplish much, if anything. There's also a possibility that I might cobble up three small adapters to run side draft carbs from a Harley EVO V-twin engine. Those carbs are the "constant depression" design that uses a rubber diaphragm, a sliding piston, and a needle valve to match the airflow and fuel mixture to the demands of the engine, like the old S-U carbs British sports cars used in the 1950s.

Now- - - -if I can ever manage to get that Chevy Trailblazer 24 valve dual overhead cam cylinder head that's sitting in the shop grafted onto a stovebolt six- - - - - -"Hold my beer and watch this!"
Jerry

Craig for what it may be worth, I agree with Jerry on this and also with Mike when he says "if you are thinking you are going to get a lot of power after modifying things, you are going to be disappointed."

A friend of mine about 50 years ago did this. I can't recall the brand of manifold he bought but it was considered the best one at the time. It "worked" but it never seemed to work properly. He tried all kind of different carburetors including Carters made for a Jeep, Rochesters of all sorts, smaller jets, larger jets, etc, etc. This was at a time when you could buy brand new Carter carburetors from any parts store. He fiddled with it for over a year...and I should add this fellow worked for a Chevy service dept. After all his efforts he admitted it was wasted time and money, went back to the stock manifold and got a Carter YF one bbl. Here are what I remember some of his complaints as being: linkage challenges, vacuum challenges, worse gas mileage, only slightly better performance, constantly ran rich and could never manage to heat the manifold properly, spitting/coughing, could not make it run lean at idle and at highway speed it would not run smoothly (it was in a 1959 El Camino, by the way).

Here is more/less how he told me the manager of the shop explained it to him: imagine your manifold as a smooth lake and first think about the stock manifold. You toss in a single rock and it makes ripples and all your cylinders suck vapor out of that single ripple configuration. Okay, not perfect because obviously the central two cylinders are favored due to their proximity to the center but now imagine this...you toss in that first rock to the left of the center point and another rock over to the right of that center point as quick as you can. Now what happens? The ripples intersect and that intersection point now produces interference and turbulence. What does that do for you? Well, it is open for debate but the GM engineers knew you would avoid that intersection turbulence with 3 small carburetors (what Jerry is talking about and what happened with the Corvette). In my opinion a 1960 235 works really well with a Carter YF3211S carburetor. It is an auto-choke, but personally I prefer that.

Good luck if you choose to go the twin carburetor direction. I think I'd talk to Jon H (CarbKing) about it.

Carl, the 1960 C10 is getting a Lugnutz prepped T5, it has a 3.90 rear gear which will remain. I have a few other things in mind for the engine, it's getting a Melling CCS-1 cam and lifters. I have an "848" head that is being machined. I have no allusions at getting 300 Hp from this engine, just a strong running engine with ample torque.

As for which manifold , well that will require more research. I understand that the carb choice will make or break this build.

One of the best-running inline six engines I've ever worked with was a 2.0 Liter Nissan Skyline (122 cubic inches) with three Mikuni/Solex side draft carburetors. The Mikuni was virtually a clone of the DCOE 40 Weber side draft 2 barrel used on various European sports cars. Six- - - -count 'em- - - -40 MM venturis! That's the very definition of "over carbureted" on an engine that size. The saving grace of that setup was a very efficient single overhead cam 12 port cylinder head with the entire Nissan engineering R&D department supporting the effort. The car was a retired racer that found its way to Okinawa from Fuji International Speedway in Japan. It also had a redline RPM somewhere north of 7K! The thing ate American V8s for lunch on a regular basis in the autocross competitions we ran when I was a member of the Okinawa Sports Car Club in the early 1970s. The body was a real sleeper- - - -a boxy 4 door sedan that was usually equipped with a small 4 cylinder and used as a taxicab. When they made it into a racer, the fender between the wheel opening and the front door was stretched out about 3 inches to make room for the longer engine.
Jerry

If you can, you should install the T5 with a stock intake and single carb and drive it to see how impressed you are with just that.
You might just stop right there.
If you do decide to then go with the dual carbs setup after having driven it with the T5 with no other modifications, you will have a good baseline to determine if the dual setup increases the performance without causing other problems.

So I bit the bullet. I found a carb, manifold and head on Ebay. I didn't give the asking price but made a more realistic offer and the seller accepted.

It an Offenhauser with 2 Carters and an earlier 235 head. I probably won't use the head but offer it up on the Swap Meet.

Got a casting number? I might be interested in the head. A pair of Carter WO carbs for a 134 cubic inch Jeep CJ-2 flathead 4 cylinder might work well with that setup.
Jerry

In the immortal words of our favorite kettle custodian: two carbs on a Chevy six is one too many or one two few!

Can two carbs be made to work? YES.

What are my probabilities???

Professional mechanic with an advanced degree in carburetion engineering and a dyno in the garage and unlimited tinker time - MAYBE 8 percent increase
Professional mechanic without the advanced degree in carburetion engineering and no dyno - break even to 1 percent increase - with unlimited tinker time, maybe 2~3 percent
Good amateur mechanic - maybe LOSE 5 percent
Shadetree amateur mechanic - maybe LOSE 15 percent

But they look great!

On the other hand, three carbs will probably make from 10 ~30 percent increase in the categories above, and with a little guidance, the shadetree dude can at least break even.

What's it going to cost?

If you "turn key" everything, maybe $2500 for the 2 carb, $3000 for the 3 carb.

Remember, you WILL NEED

Intake manifold
Carbs (either 2 or 3)
Carb rebuilding kits (either 2 or 3)
Carb tuning kits (either 2 or 3)
More carb tuning kits because you didn't get enough range the first time plus additional gasket kits (either 2 or 3)
Custom linkage
Custom fuel lines
Possibly custom air cleaners
Fabricate heat (water, exhaust, or hot air) to the intake manifold

A larger single carb will probably be less than $500, and significantly improve the probabilities listed above, but it won't look as good. Do you drive down the highway with the hood removed?

But if I haven't convinced anyone, I know a guy that can supply carbs, carb kits, carb tuning kits, etc. !

Jon

The casting number on the head is "3835517", the production date is "D 12 0".

With that casting code info, the head is from a 1942-53 216 - production date D = April 12 = 12th day 0 = 1950

Thanks Dan. I knew it was an early 216 head. The head was rebuilt some years ago and never installed. I am waiting on delivery now, the intake should be here tomorrow, and the head a day or so later. Once I have a chance to look things over first hand I will post some pictures.

The numbers on the Carter carbs is 787SB, as near as I can find it's for a "37-'52 Chevy Truck.

I happen to have read enough of Carbking’s posts to know that he recommends mechanical power systems for multi-carb setups vs carbs with vacuum power systems. For purposes of this conversation, that means something like Carter W1s over Carter YFs.

I’d like to know more about WHY that is……

1) I’m assuming that multiple throttle openings screws with the vacuum signal and requires some major recalibration to respond to a different signal. No such signal problem in a mechanical system. Your adjustment is the movement of a lever or such. Is that reasoning more or less right?

2) Let’s say one has unlimited tinker time, and even unlimited funds. How much more difficult would tuning be with two YFs (let’s just use the two Tuts59 has on the way for discussion purposes) vs a pair of W1s? Let’s use a good running 235 6 cyl as the hypothetical engine for that question.

If somebody is really interested in some Sun Electric Co. "We test- - - -not guess" research, I would be willing to donate some time on my dyno to evaluate modifications. I've been tinkering with an idea to build up a portable engine test stand on a trailer to haul around to car shows and swap meets and offer a sort of "Myth Busters" evaluation for some of the fertilizer merchants who hang out around those venues. I doubt if I'd have many takers, though!
Jerry

I was wondering if anyone has seen a 6 cylinder with three carburetors. With each carburetor feeding two cylinders. The linkage could be similar to the Honda 750. That would allow synchronizing the carburetors. That would eliminate the pulsing problem that is seen with multiple carburetors all in the same intake flow. Just trying to understand this approach. I knew an engineer that ran 2 four-barrel 1200 cfm Holley carburetors on A V6 Buick in a dragster. The competition tried running the same setup after he set low ET and fastest times in the class. Needless to say they ran horribly. He always kept the systems covered up from prying eyes. What they couldn't see was that one barrel on each carburetor was blocked off. Each cylinder ran on one barrel. It seems that running two cylinders per carburetor is feasible. Just looking for input on this approach.

1953~1955 Corvette 6 cylinder.

Jon

Jaguar, Austin-Healey, and Aston Martin, to name a few. I'm in the planning stages of using three Keihin side draft carbs for a Harley EVO engine on a stovebolt. One of those carbs can handle an 80-100 cubic inch air cooled V twin, so three should work well on a 250-something cube inline six.
Jerry

That sounds like what I envisioned. I think you will make it work. Synchronizing multiple carbs was a chore on my 69 Honda 750 due to the use of four cables instead of mechanical linkage. Cables tended to stretch at different rates. The next upgrade had mechanical linkage that solved the problem.

I worked for a company in the early 80's that designed and produced carb tuners for motorcylces. We had several customers that used the tuners on cars with multiple carbs, mostly European and British as Jerry stated. I have worked on various race engines with multiple carbs and even a few with Hilborn injectors. I have no doubt that the dual carb setup won't be a learning curve and a task to get right or at least close to right. There are many examples of the dual carb setups working on Stovebolt engines, someone has figured it out.

Look forward to seeing your progress and results, Craig!

Ambitious project. I’m confident you can make it work. We don’t often have a thread journaling this process.

So my Christmas present to myself was waiting on the porch when I got home. The manifold is as was described by the seller. I found some pulled threads where the heat riser plate mounts but other than that it seems solid.

The carbs are not numbers matching as far as model but both are Carter YF. They look to have been rebuilt and not run. The seller stated that the had been on is Father in Laws shelf for several years. They smell like an antique shop, so I'm sure it's true. The linkage is complete and moves freely. There are no missing parts and the fuel bowls are clean.

I will do a little more inspecting and note anything wrong.

That looks like a good starting point. I've got some suggestions on how to fabricate an exhaust gas intake heater if you also intend to use a Fenton-style dual exhaust setup. PM me.
Jerry

Both the 787s and the 964s are 216-application. It would be good to figure out if both were setup (both originally and current state) the same in terms of venturi size, main jet size, and metering rod. Might keep you from chasing your tail on tuning if there are internal differences that need to be resolved.

I have some literature stashed with those kinds of specs on the 2100, 2101, and 3211 (235 carbs). I don’t have any on the 216 carbs.

I bet someone here does, however.

Heavy mouth breather here. When I overhauled my 261 I wanted to see if I could get a little more out of it also. I went to Tom Langdon and he set me up with a Bulldog cam and a Nicson manifold and dual 32/36 Webers. It took some tinkering to get it synchronized (I enjoy tinkering ). Now when I'm running down the road and I put the pedal to the metal and those secondaries open up it's like that 261 goes into another gear. I really enjoy driving the old stovebolt around and that little extra power makes it even that much more enjoyable. No regrets here. Good luck with your project.

So far everything I have bee able to find says that both Carburetor's are 1937-1952 series. The one difference that stands out is the size of the "Spring Loaded needle". The 787SB has a 5/16" needle , while the 964S has a 9/32" needle. I'm sure there are other differences that I have not found. For now I want to do a good cleaning and inspection.

In general, the reason for my comments about mechanical power system carb being preferable to vacuum power system carbs boils down to two issues: Time (ease of calibration modifications, and adjustment), and cost (time is not free, and often there are special parts required that must be fabricated).

The YF is a special case, as the design of the YF allows a PARTIAL manual override of the vacuum system. Parts of this post would apply to other vacuum power system carbs, but not all. As an example the Rochester B has a power piston that can wear, a piston spring that can fatigue, and a vacuum chamber that can warp.

Keeping the exact calbration in all carburetors can be both challenging and time consuming.

It is important to keep the movement of the calibration parts, in the case of the YF, the diaphragm and metering rod, exactly the same on all carbs.

There are two issues with the YF in accomplishing the above: (1) fatigue of the lower diaphragm spring, and (2) warpage of the diaphragm housing (read Jon G.'s excellent posts on machining the diaphragm housing). The tension of the lower diaphragm spring is important, as its position is counteracted by the vacuum below the diaphragm. As Jon G. has posted, the YF pump circuit works opposite to what most would think, as the pump RISES as vacuum is lowered; activating flow through the pump jet, and raising the metering rod's position in the main metering jet.

New springs should be installed when the carburetor is rebuilt. And the diaphragm housing should be inspected and repaired if necessary.

The mechanical override of the power system is a "failsafe", and does not create the range of movement created by the vacuum system; thus the YF may be considered as a vacuum power system carburetor.

Once all of the carburetors have the vacuum systems in good working order, the next issue is the lower pump spring, which doubles as a vacuum spring. What does one do if one needs a set of springs with a different tension? How do you feel about hand-winding small precision springs?

I have done a lot of work with the Carter AFB springs, which may also be used in some of the Carter WCD and WGD carbs, and I have also done some work with the WCFB springs. I have never seen the need to do the research on YF springs (and, no offense meant, I still don't). And forget about the old wives tail of clipping coils (actually this is an old husbands tail, old wives are smarter than this!).

So, to answer JW's question within his parameters: If one has unlimited time and unlimited finances, then YES, it is possible to make the YF's work as multiples.

Would I personally do it? Maybe, if I were 60 years younger, and had ample free-time as I did then. Shoot, I actually once participated in a bowling league.

Nah, I still wouldn't do it. The W-1's are common as dirt, and so much easier to work with........

But if this post hasn't convinced those interested in doing this, I have a LOT of the 216 sized YF's that are just begging for a new home.

Jon

These carbs are QUITE different: (1) main body bypasses are machine differently, (2) main metering jets are different, (3) metering rods are different. This is all I checked; probably a lot more differences.

The 787 was released in March of 1950 as an aftermarket carb for 1937~1950 Chevrolet

The 964 was released in November of 1952 as superseding the 787 (with improvements), and was to replace 1937~1952 Chevrolet.

Jon

To add to the cost, install an Air Fuel gauge to the dash and O2s in the exhaust, it will cut tuning time in half. You will still need to know what the gauge is telling you and how to correct the problem, but when asking for help you will have numbers instead of ( it feels likes ). Seat of the pants will get you close, A/F gauge will get you on the money. I have a SpeedHut stand-a-lone gauge in my '37, everyday is a different reading due to air pressure and temperature, fuel station choice also changes the reading. Mine averages 14.7 to 15.5 running around town, mid to upper 15's on the highway. I changed metering rod depth on twin W-1 Carters by .025", the ratio went up .5 to .7 percent leaner . I have special fixtures to hold a dial indicator to set rod depth and throttle opens. Floats are set with dial calipers, I have a modified Unisync synchronizer for setting idle speed.

Just to point out how sensitive the air fuel gauge is, I sanded .005" off the metering rods second step to cure a part throttle lean out, the gauge pickup on the small change.

When we say both carbs need to be identical, you better believe it. Smaller carburetors keep the air velocity high, somewhat close in the range the carb was designed for. Add larger carburetors, the signal will be half what it should be.

I tried dual Monojets on a 250. Both carbs came off 250's from 1970, both set up the same. It ran decent, smelled terrible, ran pretty strong at full throttle, and the really neat part was you could actually see the fuel gauge moving! I switch it over to dual W-1's from the 216 engines.

This fall I install a catalytic converter just for the fun of it. The exhaust is as clean smelling as any new truck. Twin Carters from the '40s on a '70s inline six 250, HEI ignition, factory exhaust, gets 21 mpg @ 65mph running A/C at 2400 rpm, it gets better mileage then my '03 Toyota Tacoma.

Joe - thanks for checking in.

Joe is one who has proved that, if done right, with a lot of testing, dual carbs CAN work.

Jon

Good stuff!

I fully understand why it's important that the Carburetors match and work well together. I think I have a lot of headscratching in my future.

I will do some research on a matched set of W1's. If that turns into a rabbit hole I'll pursue a matching YF.

In the meanwhile the Cylinder Head has arrived. It appears to have been rebuilt with new valves. I looks as if it has set unwrapped for a couple of years. The head may find it's way to the Swap Meet as I don't have a need for it. The head was part of the sellers package.

What size are the spark plug threads- - - -10MM or 14MM? I need a 14MM 216 head with the side cover that goes all the way to the valve cover for one of my projects.
Jerry

Why don't you guys take discussion of buying/selling the head over to PM.

I'm going to shelf this project while I do some more research and locate a "Matched" set of Carburetors. I still need to acquire a Fenton header and heater kit to make this all work. This setup will eventually find it's way on to the 261 I'm prepping for "Thor". That engine will have the Melling CCS-1 cam and lifter set along with the GM small cap HEI and the PCV system that is currently on the 235.

Jerry PM sent.

Food for thought, I made a header for my 250, front port turned and ran down towards the frame getting larger as it went. Each additional port was added to the pipe with smooth transitions very much like you would see on a " dry lakes roadster " . It went from 1 5/8" pipe leaving the head to 2 1/4" down by the transmission. The exhaust was 2 1/4" to the rear bumper with a high flow turbo type muffler. The truck ran no different at all, just louder, I even went to the local drag strip when it was still around and made three passes back to back. The next week I went back with the factory exhaust system, 2" pipe, cast manifold, and stock muffler, the times slips showed no difference since the weather was still the same. The header and larger pipe went to scrap pile.

Headers only work if you run more air through the engine than the current exhaust can handle. Higher compression, way more air flow through the head, and higher rpm. The carburetor and intake IS NOT the choke point, the head is. Since I ran my engine at the exact same rpm, the exhaust didn't add any power.

My engine runs better with dual carburetors only because the cylinders are better balanced, meaning 1 and 6 are getting the same fuel mixture as 3 and 4. It has nothing to to do with more air flow or more fuel.

When I installed my stock Monojet manifold and carburetor last summer for testing, I could not get a decent A/F ratio, no matter how I jetted the carb. It ran Ok, but always showed lean, this was a distribution issue.

Adding the Fenton header is a not a must but I need to do something as the stock manifold is cracked. The Fenton would just add to the look, more "Mouth Breather" stuff.

I disagree, Fenton Headers or at least dual exhaust is a must. It just goes perfectly with dual carbs!

Sarge - PM sent.

Jon