The Stovebolt Site Forums The Shop Area Engine Shop Carter YF 4339S Size Question

Please excuse my ignorance. I'm still very much a beginner with these old trucks.

With the help of a fellow StoveBolter, I've been super lucky to acquire a 1965 rebuildable-core 292 inline 6 ("Thank you so much Karl!!!"). My plan is to fully rebuild this engine to stock specs (no Hot-Rod bling for this engine). One of the items I needed was a carb. Well, I found a one barrel Carter YF 4339S.

From my research on this forum, I've learned that the Carter YF 4339S is a good fit for the smaller Chevy 250 inline 6. Does anyone know if this carb is big enough for the 292? I'm asking before I clean this thing up and fully rebuild it.

The brain-straining I've done so far (don't laugh!): After looking at Mark Allen's casting numbers book, I see the 1965 250 was rated at 155 horsepower @ 4,400 rpm, and the 1965 292 is rated at 165 horsepower @ 3,800 rpm. So I considered the peak power outputs of these two engines as a guide. That lead me to think of these engines as simple air pumps (I know, less than ideal...). The 250 at 4,400 rpm is "ideally" moving approximately 636 cubic feet of air per minute. The 292 at 3,800 rpm is "ideally" moving approximately 642 cubic feet of air per minute. Pretty close.

Am I just wishing too hard that this carb I found will work?

And if it is too small, any suggestions on a one barrel carb I should look for? These older carbs are not so easy to find, and I would prefer to use an original one from the same era if possible.

Thanks in advance for your thoughts.

Your calculation assumes 100% volumetric efficiency, which will not happen.
The math also assumes an intake stroke on every revolution, it's every other.
Using 95% VE, the 250 needs 302 CFM.
The problem is not size, but how the internal circuits have been designed - for a smaller engine.
Will it work? Try it out.

YF4339S was made for aftermarket 63-67 Chevrolet cars (not trucks) with 194, 230 and 250 engines.
This carburetor has a diaphragm choke pull-off.
Carburetors designed for smaller engines tend to run rich on larger engines.
Before 1970, Carter did not publish CFM ratings.
The carburetors were tested my measuring the A/F at different vacuum steps.
The carburetor has an excellent 3 step metering system (rod and jet) for economy, mid-range and power levels.
My GUESS is that at idle, this carburetor will run rich on a 230 and lean on a 292.
Basically there is no one-size-fits-all carburetor without some compromise.

If you read past postings and other forums, the best carburetor for the 292 ends up in debate.
I would read as much as I can and learn from other's experiences.

I think that most agree that it is hard to find a Rochester B that doesn't leak gas or doesn't have morning start-up issues.
As far as I know, Carter only made the YF4371S which was used on 230, 250 and 292 engines for trucks with California emissions.

There are other options if you go with a 2 or 4 barrel carburetor but that requires a manifold change to do it correctly.
Bolt-on adapters to a one barrel manifold is less than optimum.

Panic,

You make it easy to see I have no idea what I'm doing. That's a good thing! It shows how much understanding I lack of all this stuff. Maybe with the right changes to jets and other parts inside, it could work. I bet the Carburetor King would know for sure. Using your ideas and math, the 292 would need 305 CFM at peak horsepower. Is this correct?

Buoymaker,

I did see the YF 4371S mentioned on the Carburetor King's site (and here on a forum post). In your experience, are there any two barrels out there that other stock running 292 users are finding useful?

Thanks for the replies.

4339s is basically a redone (to produce) less expensively 3211s.

Carter suggested it ONLY for the smaller cars (NOT suggested for use on either trucks or full size cars).

Air flow is the same as for a 235.

Main jet is fixed, thus recalibration MUST be done with metering rods, but venturi is too small for a 292.

I have posted MANY times that Carter did NOT offer a YF specifically for the 292, but one for a Ford 300 CID truck engine can be made to work well. There are several different numbers that one can use.

If I had one for sale, I would be very cautious to whom I would sell it, and for what.

Jon.

The main jet in the later YF's are fixed.

Terms to look for when researching Chevy inline-6 engines:
Log style intake manifold (also used on early Corvette)
Siamesed-port head
Exhaust scavenging - exhaust diameter
Designed for low end torque...on purpose

To some thinking, these design features are handicaps today but we at Stovebolt love our "tractor" engines.

Most of the new 2 barrel carburetors are too big for the stock 292.
The smaller base Rochester 2G (283 V8) is a reliable carburetor and may work better (I haven't tested one myself).
No guarantees on gas mileage improvement or acceleration bog.
Like the Carter YF and Rochester B, they are 60+ years old and may have serious wear issues that need addressing (throttle shaft & throttle linkage etc.).

Engine demand strongly affects carburetor flow, all CFM is rated at a specific vacuum draw: 3.0 Hg" (inches of mercury) for 1 and 2 bbls., 1.5 Hg" for 4 bbls.
A smaller-than-calculated carburetor will only reduce peak power slightly (if at all), in part because the restriction raises the WOT vacuum slightly (above the 3.0 Hg"standard for testing).
A larger-than-calculated carburetor will only increase peak power slightly (if at all), in part because the restriction lowers the WOT vacuum slightly (below the 3.0 Hg"standard for testing).

Some mixture compensation for incorrect size can be made by jetting changes, even float level adjustments, but what's your time & trouble worth?
I'd try to get the right one.

"Table 3", attached above, is my work, read it and other carburetor and manifold comments at http://victorylibrary.com/mopar/log.htm

I just love this place! The knowledge base is truly amazing.

Jon (CarbKing),

Thanks for your thoughts. I also wanted to say what an amazing resource your website is! I'm spending time there learning a lot. I will be contacting you to buy parts when I find a carb I can use.

Buoymaker,

The main reason I'm trying to keep this 292 as close to stock as possible is because I too want that low rpm torque! This engine was specifically designed and made for it. I know enough that if I take steps to get this thing to breath more freely, it will become useless in a 2-Ton truck. It's interesting that I too had the idea of adapting an early Rochester 2G from a mid 60's 283 like you mention above. The biggest problem I see is finding a good rebuildable core. These old carbs are worth their weight in gold! I appreciate your ideas.

Panic,

I've been reading about the differences in how these CFM ratings are derived for the 1 and 2 barrel carbs compared to the 4 barrel carbs. Jon goes into great detail on this subject on his website as well. I would love to get the "right" carb, but that would be a Rochester B, and, well, there is lots of heated discussion about that carburetor... This is why I'm presently searching for a workable alternative.

Thanks again gentlemen.

David I would go with Jon's statement, "Carter did NOT offer a YF specifically for the 292, but one for a Ford 300 CID truck engine can be made to work well."
Jon barks and bites when you call him on the telephone so be polite. I don't blame him. He's has had thousands +++ to call him with no clue of what they want/need.
I for one would love to know which carburetors he would chose and which parts to swap/modify even though I don't own a 292.
The beginnings of Federal emissions in 1972 so MAYBE he would use those made in the years from 1969-71.
BTW, like you, I also would prefer to stay with a 1 barrel carburetor.

Panic, I apologize for robbing your 2G table. I added your name to my copy to remind me not to do it again. Sorry about that.

The Roch. Monojet was used on 292 engines from 68 on. They work real good & have larger venturies & throats then the ones for 230-250. The one from the early 80's has electric choke
.
George

Buoy - Personally, I would not use any of the YF's on a 292. I suggested the Ford YF simply because they are readily available and cheap; and seems a lot of folks are looking for cheap. And there is absolutely no comparison to ANY Rochester single barrel as far as quality. When I made the comment you quoted, I should have stated "non-smog 292", as Carter did offer the 4371s for a smog version of the 292. Please do not ask me how to recalibrate smog carburetors; I will not do so.

On my 1979 Ford 300 CID six shop van (now has been recycled thanks to inept drivers that require salt and cinders to open the front door in winter), I removed the original Holley single barrel carb (WAAAAAAAAAAAAAAY too small), and replaced with an Offenhauser aluminum 4-barrel intake and Carter AFB 400 CFM 4-barrel. Very seldom did the engine get deep in the secondaries, but the primaries flow about what the stock single barrel for a 292 would flow; and the AFB is infinitely adjustable. With 3-step metering rods, I can adjust calibration at three different values of vacuum, plus idle.

At the same time, I removed the 3-speed manual transmission that Ford thought was necessary, and replaced it with a truck 4-speed.

Because of the Carter AFB, engine efficiency was great.

Because of the truck 4-speed, low speed power was amazing. The van would pull my loaded 16 foot trailer in low at idle.

The kicker is in the costs: Offy intake - $595., Carter 9400s AFB $1100., truck 4-speed (used) $250., new clutch and pressure plate (insurance) about $125.

But the results: With the Holley, the van never saw 12 MPG. I am not going to post mileage with the AFB, but I drove it (with a good friend who is a Chevy dude) from Eldon, Missouri to Chickasha, Oklahoma fully loaded with out stopping once (standard tank). Anyone interested can look up tank size, distance, and do their own math.

The van was finally recycled with about 450,000 miles due to rust from the aforementioned salt and cinders the third time. The cylinder head was never off the block, and the engine ran seemingly as well as it had at 100,000 miles.

If I were REQUIRED to stay with a single barrel carb, I would acquire a Zenith type 28AV12 or 228AV12, and recalibrate it to Zenith 7959 (23AV11) specs. This would require machining a new venturi, and replacing all of the jets.

When I do make a recommendation, I try to do so with all issues in mind; and my guess would be the majority would not spend what I spent on the van conversion (even though it paid for itself many times over), and yes, I did pull the Offy and the 9400s prior to scraping the van.

As far as the barking and biting.........................

It isn't the caller that has no clue that is aggravating, they are generally a pleasure to work with; it is the self-annointed expert who knows exactly what he wants and the only opinion he wants is agreement with his totally non-workable idea, and then he has someone to blame when his idea doesn't work. When agreement is not forthcoming, he wants to argue. I have time to try to answer questions, and try to help. I do not have time to argue.

Jon.

No harm, no foul, glad to help

Well David, there you have it. Full circle once again.

Criteria:
1.) Without breaking the bank
2.) Without major modification
3.) Something that looks original

Conclusion:
The forum recommends, as Panic stated earlier, the original 292 carburetor.

If you plan to rebuild your 292, I would first find an original carburetor, install it and run it on your engine before rebuilding your engine.
You will want a known good carburetor for break-in. Later on, over time, you can try other options.
If you find a better carburetor or fuel system that works better please post your solution here on Stovebolt.

Again, thanks to all who have given their thoughts on this.

Buoymaker,

I think you are correct. I love how you laid it out in three easy criteria points! We think alike. Not 100% sure I can get this engine to run before I rebuild it. I will though be using a wideband O2 sensor to sniff the tail pipe when I first fire it up, and during final tuning.


Last night, I found a rebuildable core Rochester Monojet part number 7029012. I know, I know, there are some here who think this is "Satan's Carburetor!" To help me, I have two early books authored by Doug Roe on the Rochester carbs. He has some good advice on how to get the Monojet to work. There's even a small, but measurable fan-base out there for this carb that can help me too.

According to my research, this carburetor is specifically for the 292 in a 1969 truck. It has the manual choke that connects to the bi-metal coil on the exhaust manifold (I'm not sure what that is called). The casting numbers from the intake and exhaust manifolds (from Mark Allen's book) that came with this engine, show they were used from 1963 to 1972 on trucks. So the carb should be as close to a bolt on deal as I can get. I may have to modify some linkage and/or arms to make it work. Completely within my infrastructure and skill set.

I'm sure Jon will have all the rebuild parts I need to make this happen!

Take care all!

At least it doesn't suffer from warpage like the "B" but it can be warped by overtightening by noobs. Check for warpage regardless.
Jon has the best gaskets .. period. Avoid the cheap gasket sets. Avoid old original NOS gaskets (shrinkage issues).
Jon has warned us that some new float bowl fuel valves, regardless where you buy them, may leak due to incomplete machining process.
Search for "staking the seat". It can save you a lot of headaches from flooding and leaking gaskets.

The bi-metal coil on/in the exhaust manifold and associated linkage is an improvement from the heat stove and heat tube design (automatic choke).
My opinion is that the old heat stove allows contaminants into the choke housing an is an on-going maintenance issue.
I have no experience with the Monojet but I'm guessing the bi-metal coil arrangement is used for fast idle, a convenience, until warmed up.
You could probably make it a fully manual choke if you wish.

Suggestions from a novice:
Take pictures then take more pictures as you disassemble the carburetor. You will need it for reference.
I would avoid media blasting of any type, for now, mainly because of tiny passages that can be quite difficult to clean out.
I learned the hard way and the next time I taped them up and only lightly used blasting in those areas I was sure of.
Degrease to get the heavy particles off.
Dish washing liquid, warm water, ultrasonic cleaner, tooth brush, Scotch Brite pad (carbon build-up) and compressed air.
I use Vapo-Rust for heavily rusted parts.

My Dad laid out the project on an old sheet (for white background), with the parts spread out in the order that they are removed (to help with re-assembly), then photo it.

Buoymaker and Panic,

All super helpful ideas! I will contact Jon (CarbKing) when this carburetor arrives.

I have to give some credit to "Wrenchbender Ret" for even suggesting the Rochester Monojet. Because the Monojet I found is from 1969 (my 292 is from year 1965), my fingers are crossed it will be a close enough fit to work.

The first thing I will do before rebuilding the carb, is mock it up onto the intake/exhaust manifold combo to see if anything is missing and if any modifications will be required.

I will definitely ask for help if needed.

If it helps, I've been impersonating a precision machinist now for more than 45 years. I'm a huge fan of "attention to detail." And I just love stuff that has lots of tiny parts.

David