The Stovebolt Site Forums The Shop Area Engine Shop Yep, the YF is better

Rebuilt a YF 2100 this spring I’ve had sitting around for a few years. A whole lot of family life and competing hobbies kept me from installing and running until just today.

The B it replaces was in pretty good repair. No warpage leaks from what I could tell. Also rebuilt by me a few years ago. A bit of throttle shaft wear but not too bad.

The little stumbly miss at 1000-1500 rpm’s is now completely gone. Engine will idle smoothly at some absurdly low RPM that was impossible with the B. I was too lazy to hook up the dwell tach to measure it.

The B was much more finicky to adjust with the idle mixture and curb idle screw. Had a definite sweet spot you had to find. I really can’t make the YF run badly or make it stumble on transition, unless I do something pretty extreme with the mix screw. The 1.5 turns I started out with is just about as good as it gets.

Good to know, I just purchased a used 2100 and plan on ordering a new kit. I have been dealing with a Rochester B for years and have not been pleased with the way it operates. I know several members here have offered advice on rebuilding the carbs but I am new to it so wondering what guide or manual to consult.

I’ve got the rebuild docs for the YF somewhere. I will post it and/ or forward. It’s pretty much just putting it back together the way it came apart. After a lot of cleaning and such. The metering rod adjustment takes a bit of finesse and pouring over the manual.

One very important thing to keep it kind. Carbking might well be the only source for the correct needle and seat for the Chevy application. The widely available kits have too large an orifice.

I ended up buying the correct (least wrong) kit in the Walker catalog. Re-used the original all metal needle and seat after I verified it was the correct orifice. Just used the kit for gaskets and accelerator pump.

My plan was to verify I had a decent, runnable unit, and then upgrade to Carbking’s kit.

Published with written authority from the Carter Carburetor Company:

Carter type YF service literature

Jon

Is there a vent to fill the bowl with a squirt bottle on a YF 2100s?

It would not appear there is. For initial prime of the carb I just shot some down the throat. Had fuel to the clear filter in probably 5 seconds or less of running.

I concur, I'm currently running a Carter 2101s.

My Rochester BC was fine for years, but when it was past is prime the Carter went on.
Smooth running with no stumbling.

I concur. My '52 GMC 228 came to me with a Carter YF. It ran well, but when I happened across the correct for the GMC Zenith 228 carb I bought it and replaced the Carter. Rebuilt the Zenith and spent hours tinkering with it, but could not get it to run as well as the YF. Put the YF back on have been a happy camper since.

I've contemplated replacing my Zenith 228 (sized for a GMC 270) that is currently on my 261 with a Carter, but it's running very well currently so no motivation to change until a rebuild is needed.

I know Carter did not make a carb for the 261 - does anyone have experience running a 2100 Carter on a 261?

JW51 your post prompted me to pickup a 2100S core this week. I've had the same experience with my rochestor B. I rebuilt it, no warpage, starts fine, idles fine, but a little stumble going through the RPM's just like yours did. My truck is a 49 but the 235 is a 56' so it will match up nicely.

In all transparency: still running smooth, but also running rich. Need to to some fiddling and see what’s up.

www.quadrajetparts.com has YF jets, a stock metering rod, overhaul kits and a bunch of other parts if you need then.

JW,

What is the result of the kits with the incorrect orifice / needle and seat? Will the engine run properly and just run rich at idle? Poor fuel economy throughout the range?

Someone smarter than me will have to weigh in. My understanding that fuel rushes into the bowl too quickly and affects how certain circuits of the carb work.

Many of the YF carburetors used an .081 orifice. Information I have on the 3211s shows use of a .076 orifice. Anyway, some of the cheap rebuilding kits you get may have a .091, .098 or .101 orifice. If you do a little geometry...we'll choose the .098 orifice for this...the fuel flowing through that orifice is nearly 50% greater than the .081 orifice. That is a significant difference. Your float and the design of the YF are wrong for this much flow...won't keep up nicely. If you're also using a one-piece needle in conjunction, you'll probably flood at idle, almost certainly will run too rich and your fuel economy will go down pretty much at all speeds (with the possible but arguable exception of wide open throttle). You need the spring-loaded steel needle and a smaller orifice. Other factors go into this...fuel pump pressure/volume, fuel line, etc but some of those flirt in my opinion a bit with minutiae and overall mean less than the size of the orifice. Jon (Carbking) may weigh in on this. He's posted lots of info about this topic over the years. Back when I did the study on the Rochester B, BC, etc in the 5 or 6 carburetors I used for the work I found 3 different sizes of orifice. You can see them below. I have no earthly idea what Rochester was thinking with these...the carburetors were all designed for use on the 235. Rochester never (to my knowledge) published orifice sizes but Carter did and was serious about it. Good luck!

Jon G. - well said.

I will add: bowl fuel level is basically a function of 4 major factors:

(1) float buoyancy (if you use the manufacturer's float, this will not be an issue)
(2) fuel seat orifice size (specified by the manufacturer)
(3) physical float setting (specified by the manufacturer)
(4) external fuel pressure (an acceptable range is specified by the manufacturer)

Probably 95 percent of the YF kits sold, are sold for Ford 300 CID sixes, which use the larger orifices (see Jon G. post above)

Changing the manufacturers specifications WILL result in a different than designed bowl fuel level. If the fuel orifice is too large or external fuel pressure is too high, then the float buoyancy (when the float is properly adjusted) will not balance the increased pressure seen through the fuel inlet. Thus the cheaper kits for the Chevrolet use the Ford valve, as there is insufficient volume to use a different valve.

In other words, using a FLAPS kit with a Ford 300 fuel valve means you are wasting your time trying to adjust the float!

Now - carburetion 101, lesson 3

Fuel is not "sucked" out of the jets into the venturi area. Air velocity through the venturi (at different points - SEE PICTURE BELOW) creates negative pressure (call it vacuum if you must) in the fuel wells, where atmospheric pressure PUSHES the fuel from the wells due to the pressure differential.

The fuel level in the fuel wells (same as the level in the bowl) will change the value of negative pressure required to cause fuel flow, and the volume of fuel flow.

More later, I have a meeting in 3 minutes.

Back from meeting

Jon.

I had this question in another thread, but I’ll ask it here. I see a little seep out of the bowl vent hole on my 2100s. Almost nothing. Normal or sign of an issue?

"Wicking" action of modern fuel.

A few years ago, I left the top off of a Carter AFB, sat it on "legs" on my work bench, and added fuel to the bowls to the normal fuel level.

Watched as the fuel slowly climbed the sides of the bowls and over the top.

Remember that a single drop of spilled gasoline will cover the entire garage floor

Jon

And that same drop of gas will stink up the entire garage and make my wife yell at me.

This is non-ethanol fuel. It wicks like that too?

Maybe. Personally I've tried an experiment similar to Jon's and unless you are trying to get the stuff to crawl up the side of a glass jar (and it will but not very far), you'll find it will creep up more porous metal freely. Worse than non-ethanol gas? I don't know. We don't get non-ethanol here. I can tell you VPM Naphtha will creep and spread on metal in almost the same exact fashion and maybe more so. I wasn't able to find anyone who claimed naphtha was hygroscopic. But denatured alcohol, acetone and compounds like lacquer thinner don't creep nearly as much, if any at all.

About 3 years ago I set out to find out all I could about ethanol-laced gas and why most people consider it to be the rap music of auto fuel. I wanted facts, but after a point they're not easy to obtain. And it is devilish irritating because the word "spread" will bring up lots of investment news, the term "wicking" will bring up information on Coleman stoves, bunsen burners, kerosene lamps and stuff like that. The term "creep" will bring up a lot of hoo-hah about metal creep and stories about crankshafts becoming pretzel-shaped if they're not stored upright. And more. Go try if you're curious. If your work parallels mine, you'll find some people think of the term "wicking" when they're talking about ethanol gas drawing moisture out of the air (which a few people actually believe does not occur). Bottom line is I think ethanol causes gasoline to spread more, but I was unable to find anything factual to support that idea. It is hygroscopic (absorbs water) and gasoline is hydrophobic (repels water). The ethanol gas you get at the pump will have 10% corn liquor in it and that lets it hold a small amount of water in suspension. And when the water that is absorbed gets to a concentration that is too high (and temperature has an effect on this), you get what's called phase separation. The extra water (along with some ethanol which bonds to it) sinks to the bottom in that case and that's when the real fun begins. Your fuel pump picks this water/ethanol cocktail up from the bottom of the tank and sends it off to your engine.

But back to wicking, crawling, creeping or whatever term you use, yes...I think the ethanol causes that to be worse but as I said I can't tell you why. I have a friend who is a retired doctor of chemistry. I should probably ask him why this is or isn't so.

Holy cow, we need a technical article on all of this wonderful carburetor knowledge.

We all may get lucky some day and be rid of the ethanol. Then again it's up to the government.

Reuters - U.S. corn-based ethanol worse for the climate than gasoline, study finds

Couple thoughts:

1) I used some fairly aggressive concoctions to clean my YF up. I will never play with the commonly-recommend Pine-sol solution again. It really attacked the casting and I can tell it’s rather porous now. That probably contributed to my situation.

2) Looking at the YF, that same passage that vents to the exterior, also has an outlet to the interior. I really wonder if the exterior outlet is even necessary. But the engineers put it there, so I will leave it alone.

Hi Patrick,
I don't know if we're doing tech tips any longer but we could assemble a nearly encyclopedic one for YF (and Rochester) carburetors if the opportunity ever arises.

I've decided Dawn or Ivory dishwashing soap in an old pot on the bbq grill and a good boiling are two of the best things I've found. Probably some sort of ultrasonic cleaner might be nice, but I don't have one of those.

I had done quite a bit of the Dawn boiling before I tried the Pine-Sol. There were a couple spots where I couldn’t touch the white crusty stuff. The little check ball underneath the accelerator pump was totally encased. And it took a lot of time before the old accelerator pump would let go and come out.

On a carb without the white crust syndrome, I’ve had very good results with lacquer thinner. But next time I might try the dawn thing as a stand alone first.

"(2) Looking at the YF, that same passage that vents to the exterior, also has an outlet to the interior. I really wonder if the exterior outlet is even necessary. But the engineers put it there, so I will leave it alone."

Bowl vent.

Re-read "carburetion 101, lesson 3" about atmospheric pressure.

Jon

Right, understood. But doesn’t the same passage connect to a vent inside to the “throat” of the carb?

Looks to me like the YF passage splits and goes both ways. I don’t have one in front of me, but fairly certain the Rochester B vents only to the interior.

Not trying to be obtuse or argumentative. Genuinely curious about it.

Different carburetors were vented in different manners.

Jon.

I don't have a 2100S to look at, but I do have a 3211S (the successor to the 2100 but re-designed with a lower profile and auto choke) which came to me virtually brand new except that it had been sitting in the original Carter cardboard box in Baton Rouge for over 50 years and that cardboard plus abject humidity had caused the outside of the poor thing to look horrible. Since I can't afford to replate it, I painted it with paint that is guaranteed to not have a problem with gasoline. Let's take a look at how it is vented:
1st image below shows the exterior vent hole (red pointer). This allows atmospheric pressure to be present constantly in the float bowl and this model plus your 2100S was designed not to function without that vent..
2nd image below shows the throat vent hole (yellow pointer). This is also constantly open and its job is slightly different.
3rd image below shows another style of the throat vent (a brass tube). I've heard some folks call these vents "Balance Vents." The idea here is this vent allows a compensation for the ambient atmospheric pressure (in the float bowl) and the difference caused by air flowing through the throat. Here's how I understand this: if you happened to live on the coast or anywhere else where you were at sea level, you'd naturally have almost 15 pounds of pressure inside your float bowl. But...if you had a restrictive air cleaner, due to the air flowing through the throat you will have less pressure as a consequence. If that is the case and this vent is either absent or plugged up, you will lose the balance needed (balance between internal and external, that is) and this will cause your carburetor to run richer.
4th image below shows a different style of the float bowl vent. This is a variable vent...open a bit at idle and then closed as speed increases. There is a spring-loaded appliance with a rubber seal sitting atop the diaphragm link inside which at idle sits a bit away from that vent hole and closes when you start driving. Why? Well, if you're idling you need that vent open so as to let any vapors to vent to the atmosphere. Remember, air passing through the throat at idle should be low and won't have as much of an effect. Then when you increase speed, that vent hole closes and the carburetor is designed to revert back to the internal vent scheme. And the way these were designed (at least as I understand it) is if that vent hole is open when you're driving at speeds faster than idle then you'll run too rich. You'll run too rich presumably because the pressure in your float bowl will be higher and that wasn't how this particular model was designed to operate. It was designed to enjoy the same pressure in the throat as in the float bowl. At least that's what I think. But you don't have to worry about that with the 2100S. Like the 3211S it was designed more simply vent-wise. Hope that helps.

Ditto on the YF.

I have several 235 YFs and parts that I have been cleaning to send to Jon G (sorry I'm so slow Jon) and the the warnings about the fuel valves are "right on".
I have seen valves made for Jeep 4 cylinder (too small). Valves with a retaining clip to the float. Valves that are way too big. Solid valves without the small spring and "tee".
All this probably because of the kits we buy at XYZ parts store or sites on the Internet not having the correct parts inside.
Compounding this is that Carter went out of business around 1984 and the good replacement parts have been history for a long time (Jon H. bought them all...big grin).
The Carter buyout brings Federal Mogul then Weber then Edelbrock made parts. Then comes re-designs to make parts common to fit other carburetors to save manufacturing costs.
We are trusting these companies to correctly provide what we need. Today we also have to worry about companies out-sourcing manufacturing to foreign businesses (Asia).
This leads to Jon's warning of the possible need to "stake" our seats because of incomplete manufacturing process.

Today we have Carbking's trusted parts, but I'm guessing he doesn't make the valves himself, hence comes his experience and wisdom on what to select and use in his kits.

Attached is a picture of a selection of valves with a NOS original (no longer manufactured) on the far right for comparison.
Notice the extended tube is gone and I have no idea of it's original purpose.
The new needles now have Viton tips.

Buoymaker - the following from the YF lecture in my Carter Carburetor School textbook:

"The long-extension on the seat acts as a stand-pipe for the incoming fuel, to allow any small foreign particles to settle around the extension rather than come past the needle. 'The extended type seat can be used only with the bowl covers which have sufficient space for the extension (some models do not provide for this type needle seat.)".

And thank you for the complement!

Jon

You have to check on some that you find...in some the needle was aluminum and those wear out pretty fast. They wear little rings around where they hit the seat and then they don't work well. A magnet is a good way to check.

Below are two I made last year. One is a .081 orifice, staked, spring loaded with no standpipe. The other is a .076 orifice, staked, spring loaded onto which I added the elevated standpipe (essentially a copy of a needle & seat I removed from an NOS 3211S) the only difference being the Viton tip. Honestly I've not found the Viton tipped needles to work as well as the old steel ones...even if you stake them, polish the seats, whatever. I know everyone's gone to that now, and they're okay but the original seems to work better.

Carter also tried a black in color thermoplasic valve.

Reasoning: it was lighter than Monel steel, and not magnetic.

But the sales folks that promised the marketing folks lied about the wear characteristics.

The experiment did not last long.

I still occasionally find one in my NOS stuff.

I still have about 200 of the spring-loaded new old stock original Carter valves to put in the Chevy YF kits.

Jon

Does anyone know if they put other chemicals in ethanol fuel such as volatiles to make it work. This would seem to enhance the fuel creeping.

All sorts of additives go in there. Isooctane and other hydrocarbons (aromatic and otherwise) are added to raise and regulate octane ratings...which will differ based on your altitude.

Commonly 87 octane for regular at sea level and 86 or even 85 at higher altitudes. That's because the air is thinner and you don't need as much octane. Companies like Chevron and others boast the addition of products like Techron and other branded additives which don't come rapidly to mind, and all of them add dyes, "detergents" and many other things.

And...ethanol is C2H5OH. If you look around, you'll find there are some other compounds sharing similar (by small degrees different) formulas. But like water (H2O) and hydrogen peroxide (H2O2...simply one more atom of oxygen), they'll be different enough so as not to be substitutable. As anyone who has ever enjoyed a tall cool glass of hydrogen peroxide might tell you. One more thing...ethanol is added to gas trucks at the terminal. That's because of ethanol's high affinity to water and the desire to keep as much H2O out of it as possible before it goes to the gas stations.

Do they increase the creeping? I don't know, but my guess would be yes.

And come to think of it, the water present in the gas might also increase the creeping tendency.

Dad used to add water to his Methanol/Peroxide racing fuel, depending on the humidity of a particular race day. The proper measuring device was a 6 ounce Coke bottle. With normal humidity, two bottles got added to the 8 gallon stainless steel pony keg he used for a fuel tank. A dry day got three, and a really humid day got one. He said the water would flash to steam when it hit the combustion chamber, and keep the fuel mix from burning holes in the pistons. That was on a 300 cubic inch flathead V8 running over 11:1 compression. Those engines burned fuel at the rate of 8 laps per gallon on a 1/4 mile dirt track!
Jerry

Here is a statement from a test I read about on the Internet:

The averaged results of four tests at about 70°F showed that the E10 lost more total weight to evaporation than the base fuel, but less gasoline.

This was a test using open glass containers sitting in a room. Maybe the increased weeping is more towards alcohol evaporation.