VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 235 engine, Need info on carbs for dual intake

Does anyone have experience with dual intake using 2 carburetors on a 235?
I have a 1959 235 engine in my 1946 truck I am restoring. Engine was bored .030 over, hardened valve seats, balanced with Howard 3/4 grind cam and solid lifters. I put a Ofenhauser dual intake on it and am searching for matching set of carbs for it.
I have heard that two stock Carter YF carbs will run too rich and parts to re-jet are not available.
Looking for a good solution on this.

Thanks so much

From Chevytalk, . This is just one post of many on forums where there is actual "how-to" information:


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carbking
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08-19-08 03:49 PM - Post#1503106
In response to 52chevybob

Olddad - carbking likes Carters because they are excellent carbs and reasonably priced; but he also likes Strombergs and Zeniths. They just cost more!

But the adjustment procedure is independant of the brand carburetor.

(A) make certain that you have two IDENTICAL carburetors (check that the tag numbers are exactly the same, except for the production date), and that the carburetors being used are the approximate proper size for your application. If this condition is not true, stop reading and start looking!

(B) screw the idle mixture control screws in on both carbs until they lightly "bottom". Check the carburetor manufacturer's spec for idle adjustment, and set both screws in the middle of the range. Example: if the spec is 1 to 2 turns, then use 1 1/2 turns.

(C) set the throttle positioner screws higher than normal (so the engine will start and run at a high idle).

(D) install both carburetors but NO linkage.

(E) acquire a manometer. Uni-syn is a brand name that is readily available. Try the local motorcycle shop.

(F) start the engine, and run at a high idle until the engine is at normal operating temperature, and that the chokes (if used) are completely off on both carburetors.

(G) reduce the setting on the throttle positioner screws approximately an 1/8 turn at a time on each carb until the idle approximates desired RPM.

(D) set the Uni-syn on the carburetor of your choice (it makes no difference). Adjust the control knob such that the plastic bobber is directly in the center of the column.

(E) remove and replace the Uni-syn and verify that the engine does NOT change RPM with the addition/subtraction of the Uni-syn.

(F) move the Uni-syn to the other carburetor. Adjust the throttle positioner screw of the second carburetor such that the plastic bobber is directly in the center of the column. When the carbs are synchronized, one should be able to move the Uni-syn from carb to carb with no change in RPM and no deflection in the position of the plastic bobber.

(G) if the idle is too high, again adjust the throttle positioner screws on both carbs to the desired RPM, and repeat the synchronization process.

(H) install the linkage between the two carburetors. Make certain there is NO movement of the throttles.

(I) intall the linkage from the footfeed. Again make certain there is NO movement of the throttles.

(J) with the throttle linkage installed, verify the synchronization. If adjustment is needed, remove the linkage, and start over.

(K) once synchronization is complete with throttle linkage in place, have an associate move the footfeed inside the passenger compartment to WOT, and visually ensure that the carburetor throttles also move to WOT.

(L) its play time ? ? ?

Jon.

I will add after (I) check that both throttle plates start moving uniformly with pedal operation.
Tony

Hello Mark, This is what I have on my 42 Chevy.
Edmunds heated dual intake with two matched Carter W1's, Fenton headers and cam ground to the 53 Blue Flame specs. Bored .020 over with the early solid lifters and a 10" truck clutch I also changed the radiator return inlet to 1 1/2 and the thermostat housing and used the larger truck fan blade.
This really moves the air and keeps the temp right around the 160 mark. I also kept the original 6V system,
I wanted to recreate a early hotrod or more of a sleeper as the car is an all original 42 otherwise. And boy does she sound sweet. Good luck with your project!

best regards, Brian

Mark - the SIZE of the selected carburetors is the most important criteria. Other criteria: (A) your planned operation (cruise, racing, etc.), (B) your (or your tuner's) familiarity with the chosen unit.

Virtually all parts are available mail order for either the Carter W-1 or the Carter YF. This is also true for the Carter WE, and Stromberg B series.

Jon.

My carb is a 3211S Carter YF and am looking for a match to put on dual intake manifold.

I have not been able to find a match from suppliers, (just offered replacement Rochester's), Also the ones on ebay the ones advertised as a 3211 do not have a choke.
Mine has the manual choke cast into the top casting with the venturi.

Do I need to switch over to the Carter W-1 to find a match?
I am also concerned that engine will run too rich.

Thank you guys for all your feedback.
Still looking

Mark

The one model of carb that I see tons of NOS is the Carter WA-1. Not sure the specs, whether any good or whether they would work for your application, but the base is the same and there are tons of NOS, sometimes in the $50 range.

Often to find something specific you need to search for months or more to find a match and sometimes you have to find an interim solution and then the part will appear eventually...

Mark - Carter 3211s came from the factory with an automatic choke.

Tim - There are LOTS of different type WA-1 carbs.

The 3211s should be S.A.E. size 3 (2 15/16 inch center to center mounting flange).

The WA-1's (except for the universal multi-fit) are S.A.E. size 2 (2 11/16 inch center to center).

Jon

Hi Mark,
A few comments...
1. Any engine is just an air pump. It can "process" only an absolute amount of air and the formula for determining the number is in my opinion fundamentally flawed. More on this in a bit.
2. The 235 is at the heart a dandied up tractor engine which is going to be happiest running between 2000 and 2500 rpm. Let me know if you want or need torque and horsepower curves. I know...people may show up here telling you they've run the 235 at up to 5000 rpm and you can do that for a short while. It just isn't smart to run one at more than 3500 rpm for very long unless you're happy thumbing a ride home carrying parts of your engine in a box. Please remember it only has 4 main bearings, a long wobbly crank and spindly rods that are known to break. I've seen plenty of 235 rods sticking proudly out the side of the block and it isn't pretty.
3. How much cubic feet per minute of air can the 235 process? At 2000 rpm, the theoretical answer is 166 cfm. At 3000 rpm, the answer is 199 cfm. In case you want to figure this out, the easy formula is engine cubic inches x rpm and the product is then divided by 3536. Most users of that formula will tell you to use peak rpm, but nobody around here is going to try to convince you the 235 is a high rpm motor...at least not unless they've been asleep since about 1920. But please wait a minute. I have always thought this formula was imperfect and more academic than real. Why? Well, the exhaust system restricts air flow for one thing and to a degree so does the intake system. If you think the 235 is a free-breathing engine, please let me assure you it isn't. It is more like an asthmatic chain smoker. I would use a factor of 90% (which is optimistic), so maybe 199 x .9 or 180 is the max cfm that 235 is going to be handling. Please keep this number in mind. We'll return to it.
4. The cam you've used is going to increase reversion in your engine. Reversion is the flow of air/fuel out of the cylinder and back into the intake manifold and it occurs in any engine. How does that happen? When the piston on the compression stroke starts upward travel, the intake valve is still open. Any cam which holds the valves open longer will unavoidably increase reversion and if reversion is increased past a point then the entire metering process of the carburetor can be upset. When you hear that rump rump sound, that's reversion happening and you'll have to increase idle speed to reduce reversion and get the engine to stop dying. Why? The air flow is no longer smooth but jerky now at lower rpms. You've altered things. For an engine like the 235 that may not be the best scheme because you don't want to do anything to limit airflow.

With these things in mind, here is an important consideration: air velocity across the carburetor's venturi. There is a sweet spot and that's what you want most of all. It is what the people who designed your carburetor worked very hard to attain. Obviously with 2 carbs you've just reduced the air flow to each carburetor by 50%, so the likelihood of running at that sweet spot has diminished greatly because you've re-engineered things. Remember please these carburetors were not designed by hayseed idiots. They were engineered carefully to match each version of the 235. And with 2 carburetors each of which was designed to provide up to 200 cfm (your Carter YF3211s), you now have enough carburetion to power a 470 cubic inch engine. Work backwards through the formula if you want to see it arithmetically. I think at this point you may be able to see why so many people running 2 carburetors on a 235 aren't happy with (a) their gas mileage and (b) the performance and (c) their fuel/air ratio is way down around 11 or 12 (14.7 is ideal and the lower you go from there, the richer you're running).

It is my opinion the 3211s was the best carburetor for the 235 built between 1957 and 1962, but you only need one of them. Remember I mentioned you don't need a carburetor capable of more than 180 cfm? That is your 3211s. If you want two carburetors, why bother? Go out there and do some real research. Figure out which small carburetor has been made for a 100 cubic engine and buy 3 of them. Then make adapters so you can bolt them straight to the head and run all 3 on your 235. At that point you will have minimized reversion as much as possible and you'll have just about the proper rating for each 2 cylinder group on your siamese intake. Tuning them will be a constant nightmare...just ask anyone who ever owned an MG. Good luck!
Jon

Jon - in a different lifetime (well 50 plus years ago), had lots of friends with imports. The folks with the MG's did have tuning issues, most of which came about due to cylinder head issues. The multiple carbs on Triumph, Jaguar, and the large Healys were adjust them once, and forget about them.

But I like your suggestion of three small carbs instead of two regular size carbs.

Mark - the configuration of the 235 cylinder head ports lends itself to triple carbs, not twins.

Jon.

Jon, the saying about the MG around here was you needed two of them. One to drive while you were working on the other. I (and all friends who owned these) could never keep the carbs tuned for more than a week or two despite having the head & block completely rebuilt by the best man Dallas had at the time (this was 40 years ago, by the way). We enjoyed the car but it was finicky in several ways. Particularly the electronics. What was that t-shirt so popular at the time? Lucas Electric...the real prince of darkness.

I'm not a fan of the 3 carb manifolds out there, but mainly that is because the carburetors used on them tend to exaggerate the overkill. If I look at the firing order and the low rpm range of the 235, I believe carbs mounted directly to the head would be a better answer, and I don't believe it would be all that difficult. I think I'd buy 3 VW carburetors of the type that were used on the 1500cc (or 1600cc) engines. Those should be nearly perfect in size as 1500cc equals about 90 ci. Ideas? I know you've cut up throttle bodies and done some interesting conversion work in the past.
Jon

Jon - two ways to make the intake easier to use with more appropriate carburetors:

(1) Find two junk carbs with cast iron throttle bodies, and cut the throttle bodies just below the throttle plate leaving only the flange. Weld the two together forming a custom adapter. I generally use Rochester B's for the large flange and Tillotson aftermarket carbs for the small flange. This option for the individual most interested in the lowest possible cost.

(2) (Opinion - much better option) take the intake with a flange gasket from the new (correctly sized) carbs to a professional welder (unless your welding is better than mine, which looks like the under side of my desk in the third grade ). Have the mounting holes in the manifold heli-arced full, the manifold surfaced for true, and new mounting holes to match the flange gasket for the new carbs drilled and tapped.

We have successfully used either Carter W-0 or Carter YF from the 134 CID Willys Jeeps. The downside to this is that anything having to do with Jeep starts with a $.

As to your suggestion of adapters direct to the cylinder head:

This requires LARGER carburetors than using the manifold with the balance tube.

The equation CFM = CID x RPM / 3456 [ (CFM is equal to CID times RPM) quantity divided by 3456 IS APPLICABLE ONLY TO 4-STROKE MULTI-CYLINDER ENGINES OF AT LEAST FOUR CYLINDERS. Using adapters to the head with no balance tube effectively turns the 6 cylinder engine into three 2-cylinder engines; thus voiding the use of the equation without modification. As a starting point, multiply the necessary CFM from the equation by the fraction 4/effective number of cylinders. Thus a starting point for the 3 carbs with no balance tube would suggest doubling the CFM obtaining by using the equation.

Initial adjustment, once one becomes proficient in the use of manometers, is not overly difficult. Tuning may be more difficult, as the A/F requirements are more stringent with this type of manifold. Of course, that old hillbilly in Missouri with all of the tuning parts just loves this While it is probably possible to milk the maximum amount of power from the engine with this arrangement, most enthusiasts are not willing to spend the time/cash for the extra few percent.

The largest issue with trying to use a three-carburetor manifold with the stovebolt seems to be that in many cases, one runs into clearance issues.

EDIT: oh, and you did bring up Lucas Electric. Their claim to fame was the invention of the three-position light switch......off, on, flicker

Jon.

Jon most of the Lucas switches I had were off, on, smoke. There was another joke...why do the Brits drink warm beer? Because Lucas Electric makes their refrigerators.

Thanks for the thoughts on the carburetion. I was going to mention the Jeep carbs but you're right. Begin the search with a $ or two. The A/F would be more stringent, wouldn't it? Probably be most efficient and certainly you know I'm talking about cost efficient to just go with a stock manifold and a 3211s, right?
Jon