The Stovebolt Site Forums The Shop Area Engine Shop Carter YF running rich? A surprise for you...

I've got a completely unexpected situation, but this is information which may be important to you and should be checked if you're rebuilding a YF. A YF3211s of mine was running very rich. This is the same carburetor I mentioned a few weeks ago was missing the vacuum bleed hole. I thought at first that was the whole problem, however it turns out the missing bleed hole was only a secondary problem. The primary problem was warpage of the pump/diaphragm housing and this was the first time I had ever seen it. However I think there's a chance it might be more common, hence this post.

There are 4 screws holding the housing in place and overtightening of these can cause the housing to warp. When this happens, the vacuum that is always present at the bottom of the diaphragm will suck gas out of the float bowl, underneath the diaphragm and straight into the intake manifold. For a couple of reasons, this will make your YF operate poorly...and it certainly isn't limited to the 3211s at all. Let's take a look. The first four images below show some of the YF housings (or bonnets). One is an older type which is flat on the bottom, one is a newer type which has a raised ring on the bottom and the other is another older type which incorporates a couple of jets and a spring-loaded check ball. Then the final image shows the diaphragm well and the vacuum hole at the bottom of that well (at about the 11 o'clock position). On to the next post due to image limitations...

The power circuit of the YF is both mechanically controlled and vacuum controlled. Unlike the Rochester it lacks the wonky power piston and relies on a simple and effective metering rod of different diameters which rides in the main jet (you can see it at the 12 o'clock position in the last image above). Vacuum pulls the diaphragm downward against a spring's pressure and unlike other carburetors, when you accelerate, the linkage pulls the diaphragm UP instead of forcing it down. In the down position, the thickest part of the metering rod is inside the main jet and so the leanest mixture exists. As speed increases, the linkage mechanically moves the metering rod up to expose the smaller part of it in the jet and when more power is needed (and vacuum falls), the rod is pushed upward by the spring. But if the housing in question is warped, that constant vacuum will suck gas right out of your float bowl all the time and especially on deceleration. You may be thinking (as I did) "There's only a shade over 1 inch between the center holes of those 4 screws, so how warped can it be?" The answer is it can be more warped than you would expect. Let's look at what I found on the housing in image 1 above. In the first image I've set the housing on a known flat piece of metal and you can see there's .006" of clearance at the middle. There's actually more in dead center, but my blade is 1/2 inch wide so that skews things a bit toward the lower side. Three sides suffered warpage of .006" and in the second image below you see there's .008" of clearance. The 3211s I mentioned had a bit more than this and that much space times 4 sides equals trouble. In the third image below you can see a bonnet I removed from a NOS 3211s I own and it also suffered some warpage (not enough to worry about...002 to 003", but it suggests that took place when the carburetor was manufactured). If you look at the 4th image below, you can see where you may also see fuel on the outside of the carburetor body if this is happening. Along the rear gasket between the throttle body and float bowl (also in front by the number stamp) and also down the back side of the throttle body below or around the shaft. You can also see residue on the carb spacer at the rear.

To correct this I got a known flat piece of wood and set a common file on top of it. And then slowly and very carefully I drew the bonnet across the file until all 4 sides were flat and smooth. After I put it back in, the carburetor is running much better now and without any of the richness issues. If you have any questions, please let me know.

My Dad taught me a neat trick to true a piece of metal; take a pane of glass, wet it, and lay down a sheet of sandpaper big enough to do what you need. Then using a figure eight pattern, sand the part until all the high spots are gone. I did this on a cover over an accelerator pump on a previous car I owned and it worked perfectly. Unfortunately it won’t work in all cases, such as yours Jon where you have a bump out in the way.

Lee.

Thanks Lee, I learned that same trick also. But as luck would have it, the one with the problem had that bump in the middle. The really interesting thing about this was that if you (or maybe 100 different people) took that bonnet out and felt of it, looked at it even carefully without using feeler gauges and a known flat piece to check it...you would probably have been willing to swear under oath that it was nice and straight and flat. But it wasn't. Overtightening is what caused the deformity. This piece needs to be snug but not tight to the point of warping.

I have seen rebuild kits with an extra paper gasket which is the same pattern as the diaphragm. My YF2100 does not call for that gasket so I never used it.
I wonder if that gasket would solve an issue such as yours. It is not a paper thin gasket. It would seem to have enough compressive characteristics to compensate for some warpage.

I've seen that gasket in a couple of YFs I've disassembled and I'm now wondering if that's what allowed the warpage? You're right...it isn't paper thin. Some of the screws you'll find seem like they were tightened by an air wrench. If an extra gasket was in there it might let the corners go down further as it is compressed causing the warpage in the center of each side. Thinking about it, that gasket would cause another problem, too. It will raise the bonnet by the thickness of it (1/32 or 1/16" maybe?). That will raise the top collar of the bonnet by the same amount (which governs where the little clip on the diaphragm rod stops) and if the metering rod isn't adjusted downward by the same amount at that time, then it will fail to hit the bottom of the jet well at the proper time. That will throw the rod out of kilter by that amount, so the step from low speed to mid range to the richest setting will take place sooner...meaning you'll be running richer as the rod is pushed upward. No, it doesn't appear in any of the Carter data I've seen. I wonder if that was somebody's answer to this problem. Sort of like the people who try to compensate for the Rochester B and BC warping by using 2 gaskets stacked on top of each other.

It was an aftermarket "fix" (Baldwin-Washington part number 20-2989) which (opinion) would make the warpage worse. Carter did not use it.

For sealing purposes, the thinnest gasket is virtually always the best.

Jon

Thanks Jon. Do you know when that "fix" was developed? We agree, it can only make things worse.

But here is what I think is a good solution. Sometimes when my mind relaxes, interesting visions appear. And this afternoon I was looking at another Carter YF which suffered this same warpage. No funny little gasket there, but the screws holding the diaphragm bonnet were too tight. And in this one there were some casting irregularities that caused one edge of the bonnet to have a high lip.

Get a 1 inch Forstner type bit and a known flat piece of wood. Preferably hard wood, but I used a piece of scrap poplar which isn't very hard but nice and flat. Drill a hole about 1/4 inch deep as you see I've done in the first image below. Now get two pieces of sandpaper. I used wet/dry, but you probably could use other types. The first one...and here I used 220...cut so that a bit hangs over each edge of your wood and use a box cutter to cut out the hole in the middle. Now holding the paper on, take your bonnet and rotate it in the hole, pressing down on two opposing corners and trading positions as you do so that you don't just put pressure on two points. Do this until you see the surface is looking smooth. Now repeat using fine sandpaper. I used 600 grit for the second pass. And now you have a surface that is enviably flat and smooth. As in the second image. I thought about Red Green while doing this, fyi. Now clean any abrasive or metal particles out very thoroughly and you're set.

Okay, once again the images changed position when I posted this. Please swap one and two in my description.

I'm bringing this back up because one gentleman is having trouble with his idle adjustment screw and this could be associated with that...

I'm bringing this back up. A gentleman here asked me why his YF2100S was leaking fuel down when the engine was turned off (making it hard to start). Please see 4 images below for suggestions. In the first image, you see the recessed area inside the float bowl where gasoline must not be present. This bears a bit more explanation, I think. Your diaphragm (rubber) is sealed against the recessed area by the diaphragm bonnet. Now when your engine is running, manifold vacuum will be present in this recessed area. That vacuum is what raises and lowers your metering rod in your main jet...providing the "power circuit." Lower manifold vacuum (when the engine is under load) allows the spring to pull the diaphragm and also the metering rod up. This means the smaller portion of the rod is in the jet and that provides more gas into the engine for more power. Then when manifold vacuum increases back to normal, the diaphragm is sucked back down, the larger portion of the metering rod is forced into the jet and your engine gets less fuel and runs leaner. INCREDIBLY MORE CLEVER and predictable than the Rochester B's oddball power piston system. Earlier I explained that a leak in this area would make your carburetor run richer and that is a bona fide fact. Manifold vacuum will suck whatever fuel gets in here right into your intake manifold and if your diaphragm isn't sealed properly the vacuum will draw fuel into this area. And about the leak-down problem? Same thing. Please look at the second image. You can see a white twisty-tie sticking through the diaphragm vent (or vacuum if you please) hole through the bottom of the float bowl. And if you look at the third image, you see where the white twisty-tie goes back into the float bowl...and into the area where vacuum will be sucking against your diaphragm. So any fuel which runs between the bonnet, the diaphragm and the float bowl will pool in this recessed area but only long enough to make its way back into your manifold. The fourth image shows once again the areas which must be checked for level when your carburetor is rebuilt. Since I posted this, I've rebuilt a handful of YF carburetors...maybe 7. Over half of them have had warped bonnet pieces. All (in my opinion) from heavy-handed or ham-fisted screw tightening. And it must be said that the little gasket provided by the cheap rebuilding kits only makes matters worse. That gasket allows more room for the bonnet to be warped...as each screw is over-tightened, it pulls the corners of the bonnet down while allowing the center area to remain high. One bonnet was defective from the start. There was a casting flaw which had not been noticed when the carburetor was assembled and I think that's why the inside of the carburetor looked like it had never been used when I got it. Hope this is helpful. Please contact me with questions. Someday I hope we have a tech tip about this stuff or at least a sticky note to make it easier to find information...

And one more thing I didn't specifically mention...but I should have. A gentleman asked me this morning if this condition caused problems at all rpm ranges and it jiggled my old memory a bit. The answer is yes, by the way...and for 2 reasons. When your diaphragm doesn't seal on the bottom side, you not only suck fuel through and into the intake manifold, but also you have less vacuum than the Carter engineers intended should be present to regulate your metering rod. So, naturally it doesn't get "sucked down" as far as it should (except possibly during deceleration), and this causes the thinner portion of the rod to be inside the metering jet...making it run richer for a second reason. If anyone needs more information on the little straightening jig/tool I made to flatten the bonnet, please let me know.

Did you have to shorten the screws any once you trued it up? I can’t imagine they would bottom out removing just a few thousands, but thought I’d ask.

One machine shop where I worked had a big hardened steel surface plate with a crosshatch pattern of grooves a few thousandths deep in it. We used it with fine grit valve grinding compound in the grooves to lap surfaces to become totally flat.
Jerry

The screws seemed to all have plenty of bottom clearance. What Jerry mentioned would be really nice to have, but lacking anything like that I just took a nice flat piece of wood (think it was poplar) and used a forstner bit to drill a 1 inch hole about 1/2 inch deep. Then I cut a circle in a piece of 120 grit sandpaper and another in a 400 or 600 grit piece and used that to make the bonnets flat on all sides. So far it seems to work like a charm.

One could also just Put it in a 4 jaw chuck on a lathe to do that, or a fly cutter on a Bridgeport!

Ed

I have been having trouble with two YF 964S, flooding. Fuel pump is glass bowl style, pressure in the 2-4 pound range. New fuel tank, cleaned the carb, one good rebuild kit, one from parts on hand. I check the fuel accelerator bonnet and did the flattening trick to get a good surface. Reassembled with no gasket. Floats set to 1 1/4 drop. Floats do not leak. With no excessive gas the 216 starts easily. I gave the top of the carb body a few passes on the flattening block as well. Is there a way to confirm that the needle and seat are correct? Is there anything else that could cause flooding? I have been switching each of these out after cleaning in carb cleaner and blowing them out with air. I have carefully checked the assembly process to insure I had the together correctly. I have screw in fuel filters on the the carbs. I want to go over all the options before trying to get one to work again. So anything I have missed?

Mike, do you have the spring loaded needle? You should...it should be a steel needle drilled out to hold a spring and a pin (which naturally rides on the float piece at the end). If you have the neoprene tipped float with no spring loaded needle it can cause problems like you mentioned. And if you have the neoprene tipped needle which has been drilled to use the spring loaded needle, it can cause the same problems. Please look at my attached image...that's what you ought to have. Also the seat should have the elevated standpipe. Also you must have a seat with the proper diameter of fuel orifice. Unfortunately I don't have data for the 964S. The 235 YF models almost all (but not the 3211S) used .081". I've learned the 3211S will run fine with an .076" orifice but with .081" it will flood or have that constant rich misfire...especially at idle and lower speeds. At higher speeds, it will simply run rich. Please let us know.

You can see in the attached image below I made what I hoped would be an alternative to the steel spring loaded needle and the stock seat (with standpipe riser) a few years ago. It didn't work, however. Even though it seemed like it would, something caused it to be less responsive and close a bit too slowly allowing too much fuel in the bowl too quickly. I tried the same strength spring as the original (even tried the original spring) but it didn't help.

I have the spring loaded needle, both are steel. I do not have the seat with the extension tube. I have a new one from a kit, the number 31-560 21H3 is on the package. It does not have the tube either and is rubber tipped.

31-560 Walker Products fuel valve that has an .091" orifice.

A .091" orifice is for a YF used on a large Ford 6 cylinder...think it was a 300 cubic inch engine. Way too big, but that's what they put in all the cheaper kits. You'll flood the tar out of a 216 with that.

The standpipe (extension) alters the flow dynamics and gives incoming fuel a little bit of an obstacle course...

Thanks all. I will experiment with one I have in my collection. And the find the right one.

I don't understand why the larger orifice would cause the carb to flood. Seems to me that when the float was lifted enough it would close and reasonable size opening as long as the needle would cover the hole. What am I missing?

Bill - the fuel level in the carburetor bowl depends on:

(1) fuel orifice in the fuel valve seat
(2) buoyancy of the float
(3) inlet fuel pressure
(4) the static setting of the float

The inlet pressure is stopped by the closing of the valve attached to the float IF the float buoyancy will overcome the inlet pressure on the load side of the seat. The seat orifice will effect the pressure on the load side; thus too large an orifice can cause the force on the load side of the seat to be greater than the force exerted by the buoyancy of the float, and the float cannot completely shut off the inlet fuel.

The correct orifice seats are readily available in the better carburetor rebuilding kits.

Actually, the 0.091 Walker valve is better than most of the cheap kits which use 0.101.

Jon.

I understand and agree with your description above Jon, I just find it amazing that the difference in "push" on the needle through the two different seat sizes would be that critical.

Using 4 psi of pressure at the carb inlet, the .091 seat would apply 0.026 pounds (11.8 grams) of pressure against a closed needle while a .101 seat would apply 0.032 pounds (14.5 grams) of pressure. Not a lot of push.

It doesn't take much.

100 years ago, the carburetor companies specified a FUEL level (not a float level) at a specific pressure WITH A SPECIFIC ORIFICE FUEL VALVE SEAT.

Somewhere along the line "mechanics" got too cheap to buy the correct tools, and/or to lazy to make them.

Also, 100 years ago, Stromberg (and probably others) actually specified different orifice valve seats, depending on the distance from the carburetor to the fuel feed (gravity feed).

Many of our customers place carburetors on a different engine, or live at high altitude, and call us for jetting recommendations. We always tell them to build the carburetor stock; then adjust the fuel level in the bowl by 1/32 of an inch; as this change will approximate 1 jet size. This way, an enthusiast can do preliminary testing WITHOUT having to buy as many different jets.

The corollary to this test is how critical using correct parts, and correctly adjusting the float setting is to an engine running correctly under normal conditions.

Jon

Bill it is sort of like firefighters using a big fat hose vs a garden hose. Not quite that simple, but everything I've learned about this (only 55 years so I'm still learning) is that a too-large fuel inlet orifice will definitely make a difference in the way the carburetor runs and everything in there was designed for a certain balance. In fact, years ago when I did my comprehensive Rochester B study for this forum, I discovered the 5 Rochesters I had bought had 3 different sizes of fuel orifices...for no identifiable reason whatsoever. Please see the image below. Hope this is helpful.

Thanks guys. As you say, it makes a difference. I understand how these small changes make a difference to flow as in a jet in the carb, but not so much in the needle and seat. I'm just amazed at the small change it takes from good to bad there.

By the way, my '52 GMC 228 3/4 ton flatbed came to me with a Carter YF 964S. Starts and runs great (avg. 14.7 MPG) except for when air temp is above 90F and shut off hot and allowed to set for 10-15 minutes. Wants to flood, but will start after 3-6 seconds of cranking.