Technical Dual Carb setup help

Hi everyone. So I'm getting ready to do a dual carb setup on a '61 235 that is going into my '53 Chevy 210. But there is one issue and I was hoping someone here might be able to provide some insight.

The carbs I'm using are both Carter YF 964s single barrel with manual choke. They are going onto a Fenton duel intake. All the parts numbers match except for the throttle bodies. One has # 788 stamped on it, the other has # 630. The diameter on one is slightly bigger than the other. I took pictures of me measuring it and it looks to be about .06 of an inch difference.

So my main question is, can I run these with the different throttle body sizes, or do they have to be exact for me to not run into problems? I've been told by some that it should be fine. I was told by a friend that I should put the "bigger one" as the main and run then in series. I'm trying to find some good answers, before I have to buy another carb off eBay for parts.

I'm new to a lot of engine work, this old car being my first that I'm restoring, so my knowledge isn't very good yet. Thanks for any help or advice offered.

 

Well you got a pretty damned good eye to be able to see .06 on a tape measure.

Check the numbers and the CFM ratings. if they are rated the same run 'em.

 

.0625 = 1/16" , any decent carpenter can see 1/16".....

 

LOL I posted this the other day but it bears repeating I suppose. Especially since carpenter came up.
I worked with an old machinist in the south when I was traveling around, he used to say, "Well you can't teach a carpenter to cut meat."

 

Bolt them up and run them, don't do progressive linkage. There is a plenum under the carbs that will sort things out re: different cfm's.

 

I'm bad with measurements. Hence the pictures.

 

<Turns on the CarbSignal>

"Looks like a job for Carb King!"

<Waits for @carbking to respond>

 

Carbs are funny animals. Sometimes ****erfly diameter is not indicative of performance. It will ball park you for sure but venturi shape and size makes a lot of difference. that is why I said to find the CFM ratings of both carbs.

 

I have a Question for You............are you Running Dual Exhaust.???

just my 3.5 cents

Live Learn & Die a Fool

 

True that, and there are eleventy-seven different versions of these, and that is presuming that the base and body are still factory matched.

 

Haven't decided yet but I am putting the cast iron Fenton exhaust manifolds on so I'll have the option.

 

How do I find the CFM ratings? Is it something that would be marked or stamped on the crab itself? Or do I have to research it online?

Like I said I'm very new to working on engines so sorry if I don't know stuff.

 

Those carburetors will end up fighting each other on a duel intake.

Your best bet is try the model numbers online to see CFM rating. You want both carburetors to be the same size.

 

I run dual Carter W-1's and have for some time. You need both to be just the same, right down to the way they are adjusted. I can tell on mine if the metering rods are different hight. I also run a wide band air fuel gauge, so even a slight adjustment shows up. I changed mine one full point leaner with a .040" hight adjustment of the metering rods. I had to use a dial indicator to get them that close to each other.
You will need to synchronize the linkage and throttle stops, plus metering. If one carb is bigger, it will likely run leaner then the other due to air velocity, or lack of it. The plenum of the intake will not equalize the carburetors. The YF is big enough to handle the whole engine alone, two will run, but the mileage will probably suffer. I ran dual Mono-jets for a while, like yours, each carb was plenty on its own, but together it ****ed fuel like crazy. Don't try to run progressive either, the placement of the carbs will result in lean cylinders at the far end.
Ideally you want carbs with about 2/3s of the needed cfm for the rpm in which you intend to run. On my 250 inch engine, the small W-1's are perfectly sized.

Dual exhaust is not needed if the rpm range stays the same. The real advantage of dual carbs is to equalize the intake runner length.

 

Research on line. Spend some time with google and you will find a list out there somewhere with the carb info.

I don't thik he receives PMs but if you go to @carbking 's profile you will no doubt find a way to contact him, probably through his web site or something. he has forgotten more about carter carbs than I will ever know. he can probably help you a lot with CFM ratings and setup.

 

If you are NOT going to Run Dual Exhaust than in my opinion you
will not do anything by running Dual Carbs.!
Just my 3.5 cents

Live Learn & Die a Fool

 

Perhaps it depends on the single exhaust. A single can be made to perform just s well and sometimes better than a dual.

 

Yup. Scavenging is not an art, it is an actual science.

 

I would match one or the other. If you run into a mixture problem "which one is causing the problem" ????

 

Unless I'm reading your post wrong or looking at your pic's cross eyed I'm seeing almost or damned close to 3/8" or .375" difference on your stretched out tape measure.

 

My answer get's back to the Basic look. I would want them to be a Visual match as well as matched in what they are doing and delivering. Without the visual match your going to have the same knot head questions to answer every time a new person looks at your motor. You can make anything sort of work. If you want it to work well and smooth you already know the answer to should you or not find a mate.
The Wizzard

 

fuel mileage ...... cool factor. Take your pick

 

Carter YF 964s is a replacement for a Chevrolet 216 CID.
Carter YF 788s is a replacement for a Chevrolet 235 CID.

If both are stamped 964s, then it would appear that Dr. Goodpliers (the evil twin of Mr. Goodwrench) has been breathing on one or both. Not saying they will not work on a two carb setup; but I WON'T be the person that tries to make them work.

You may (or may not) find this reference useful: http://www.thecarburetorshop.com/Dual1barrelcarbs.htm

Jon.

 

A general comment about CFM ratings (since the subject surfaced in this thread):

Please read the link first: http://www.thecarburetorshop.com/Carbshop_carbsizesandCFM.htm

Carter flowed all of their carburetors (I currently am the caretaker for these do***ents). Carter DID NOT PUBLISH CFM ratings for most of their O.E. carburetors before approximately 1970. They also did not publish CFM ratings for any except universal aftermarket 4 barrels (4758s, 4759s, 4760s, 4761s, 4762s, 4846s, and 4847s) before approximately 1970.

Before anyone asks - IT IS IMPOSSIBLE TO DETERMINE CFM RATINGS FROM THE FLOW TESTS THAT CARTER DID ON O.E. CARBURETORS. I had this discussion with the Carter engineers when there still were Carter engineers. Carter did the flow tests to determine A/F ratios at various vacuum steps, not to determine CFM.

And if one reads the link, CFM should be treated similar to a vector rather than a scaler number. I realize CFM does not have direction; but the value is determined as much by the rating method as by the actual flow rate. Discussing CFM of a carburetor without knowing the rating method is as useless as trying to argue with the IRS

Jon.

 

They are both stamped 964S. The one with the 788 throttle body is what was on the motor when I bought it, the other one I purchased off eBay. I'm ***uming my best course is to try and hunt down another 964s with that same number throttle body? Or should I try and hunt down a matching throttle body off another carter from the era? Either way it looks like I'm gonna have to buy another carb regardless, working or for parts.

Also thanks for all the info. It helps a lot.

 

OR should I ditch the dual carbs and go to a single. This 235 is replacing a 216 in a 4-door '53 Chevy 210. The car is going to be a daily driver and will be driven a lot, but I'm not looking to race it or anything.

 

This question, and answer, are yours, and yours alone.

The duals, if done right, may add 8~10 horsepower to the engine. Not because the engine is under-carbed with the stock carburetor, but because the duals will provide a more constant volume of fuel to all cylinders, thus somewhat improving the volumetric efficiency of the engines. They also look good if you have the hood open at a show. And, again, if done right, may increase your fuel economy by 5~8 percent. And they will be as reliable as a single carb for a daily driver.

The single carb will run the engine well; the duals can do a wee bit better. Your call.

Jon.

 

My tool maker eye see's about 3/16 or .187; but I did cheat and counted the lines..

 

Hot Rodding 101....
Start with stock. Get the stock engine (235 to clarify) tuned to perfection. Then and only then do well researched and well prepared performance upgrades.
Do these upgrades one at a time to actually see and feel the results. Start simple and move to the more complex.
I dare say that a stocker "that's right" will out perform most engines that have all the "goodies" thrown at it.
Besides....putting a full pressure 235 in a 216 car makes a hot rod.

 

If you will be using the Fentons, make sure to provide some heat to the dual carb manifold, similar to stock. Additionally, the look may not be to your liking, but many years ago I ran Fentons into dual pipes, with an "H" pipe connector, both pipes run down the driver's side clear to the bumper. Great sound, & very smooth running.