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Carburetor 38 Century


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Hello All! Need your expertise once more regarding the correct/better carburetor for a 38 Century with a 47 fireball engine... The electric choke was all over the place and wonder just how worn out that old carburetor is... Am I better off starting with a brand new unit? or should I just remove it and send out-try to salvage? I tried to adjust the mixture/idle and the car run better, but could not get into the choke system... Photos below.

 

 

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Simple Stromberg AAV, common to Buicks for many years. Our friend on this board Carb King can provide a rebuild kit or there are many rebuilders out there who can rebuild it for you. Not a big deal and buying an NOS carburetor isn't a guarantee of perfection--in fact, an NOS carburetor will likely need a rebuild, too. Chokes are adjustable and there are detailed procedures available in the factory manuals for setting up the carburetor properly. Not a big deal at all.

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The original carburetor on a 1938 Century would have been a Stromberg AAV-2 or a Marvel CD-2B. That car appears to have a later Stromberg. It is not that unusual to find cars with later carburetors. Any competent rebuilder should be able to fix that one. If you want perfection, you could probably buy an original AAV-2 and have it rebuilt. I did that for my 1938 Century project.  

 

If you look closely at the base of the carburetor you will see the Model number on the base.

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Darn your eyes are better than mine Matt, thank you!... Did not see the model # from the photos!.. I will get a kit and try to find the info on the choke to see if I can fix/adjust... If I am not able to get it right I will consider a  professional rebuild or replacement. If the AAV carburetor is better than the correct one, I will use the same model. Just want it to work right... Do you know the initial set up for the mixture screws? 3 or 4 turns from seated position? Does the screw on the right control the low/high circuit, or how is this designed? Thanks again...

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I can't read the model number in your photos, but I know where they are located. AAV is the basic series, but you will find some additional numbers after AAV to identify the exact carburetor. I don't have any idea about the settings of whatever carburetor you have. The 1938's original Stromberg AAV-2 is a good carburetor but the original chokes are often problematic. I have no experience with the Marvel CD-2B. I know my 1937 has a slightly later Stromberg but my 1938 has the correct AAV-2. If you start trying to switch carburetors, you have to be careful that they are actually compatible, not just that they are AAV series and appear similar. 

 

You need to get a 1938 Buick Shop Manual.

 

The service manual has information on the carburetor but a later carburetor will not be included in the original manual. I am sure that a Google search on the complete carburetor model number will probably help you find some information on the carburetor.

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8 hours ago, philipj said:

Hello All! Need your expertise once more regarding the correct/better carburetor for a 38 Century with a 47 fireball engine... The electric choke was all over the place and wonder just how worn out that old carburetor is...

 

 

As you have a 47 engine the carb may from a 47

https://www.teambuick.com/reference/carburetor_numbers.php

 

Does not have an electric choke.  The electric vacuum switch is for starting, if fitted (Could not see in the photos)

 

Download the 1942 Buick shop manual. All of it section by section. The pdf link does not work.

It is very comprehensive and has information that can be used with all straight 8’s.

It has more information than was included in older “Shop Manuals” before 1942-41

http://www.oldcarmanualproject.com/manuals/Buick/1942/Shop Manual/

 

And https://www.teambuick.com/reference/library/52_shop/index.php

Edited by 1939_Buick (see edit history)
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Hello there,

 

Thank you for your help here... I will take  look at the links provided..  Wish I had better photos, but the second shot partially shows the choke with what appears to be a wire going to it. Curiously, this is not set up with the solenoid (Sorry don't know the exact name) that sits on the intake manifold with 2 wires going to it that is seen on so many models... I will leave everything alone unless it does not work, I do not want to reinvent the wheel here.

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The identification number necessary for carburetor identification, and to order the correct rebuilding kit is visible in the third picture - 7-?? Looks like maybe 7-57, but you should be able to read it.

 

One of the easiest of all carburetors to rebuild. The only"gotcha" is that SOME (not all) use a left-hand thread on the fulcrum screw holding the pump arm. If it seems very tight, try it the other way.

 

Jon.

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Hello Jon,

 

The number is 7-57... Is that the month and year of manufacture? How much do you normally charge to rebuild a carb like this? Bt the way, both the mixture screws were set about 3-1/2 turns from the seated position... I have a feeling that the one on the right might need an extra turn? High speed circuit? Thank you..

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Each set screw adjusts that barrel of the carburetor. Two barrels, two screws. They are primarily for idle and low-speed, the high speed metering is handled internally by the jets. The manual will describe a basic adjustment, but 3.5 turns out sounds about right; if anything, it might be too far out (which richens the mixture--what does the exhaust look/smell like? How does it sound? Smooth or snuffly?). Jon will be able to tell you much more, but don't be afraid of a rebuild on one of these, not a big deal. Adjusting will be critical to get best drivability and you'll play with the screws and quickly learn how they affect the engine. You will likely need to adjust timing--my Limited likes about four degrees more timing than stock, which is OK because we have high-octane fuel (it was designed to run on 71 octane). Moving the timing required some additional carb tuning, so it's a fussy project, but certainly not difficult or beyond the means of a guy working at home. It's just a time and familiarity thing, that's all.

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7-57 designates a carb from a 1942 60 series.

 

We no longer rebuild (too busy with the manufacture of rebuilding kits). We do manufacture a rebuilding kit for this carburetor.

 

The idle mixture screws should not be out anywhere near as far as you have them. One turn is a good starting point, and they may need one and one half turns for a very worn engine. Anything more than two is out of range. Probably means the carb is partially clogged, and needs to come apart and be cleaned.

 

Jon.

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Hello Jon,

 

Thank you for the information here.. The car was running very rich, so I leaned out one screw from 5 - 1/2 turns to 3-1/2  to match the other (inboard) side and also opened the idle a little.. Run without black smoke and was peppy but would often stall out while driving... At that point I run of time, and without any info I left it there... I cannot tell 100% if the choke was working properly, but the car was very smooth, except for the black smoke under load and stalling while driving intermittently... Timing and a complete tune up came to mind, but I know the carburetor needs to come off and be rebuilt at best... 

Just curious, what is the cost of a new 7-57 carburetor and rebuild kit? Thanks again.

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I thought someone else might have mentioned it but no one has.  It looks like the inlet fittings both have some kind of sealer or teflon tape on them.  This might be why some things are plugged inside.  I was always taught that one should never use any type of thread sealer on this type of fittings.  If the don't seal themselves then you either need new fittings or a new housing, no exceptions I was told.  Not specific for this carb or any specific car just general proper mechanics.

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I did notice that paste and wondered also... I have only and very carefully used teflon tape on fittings threaded in the correct direction to avoid problems... Maybe something is really clogged up! Thank you for pointing out something I should not have ignored...

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No offense, but no real reason to buy a new carb (that would STILL need a kit!).

 

These carbs are virtually bullet-proof, and if you can read, the service manual would get you through a rebuild.

 

A major rebuilding kit made-in-USA with shipping is less than $100. if you live in the lower 48 states. Less expensive kits with fewer parts of unknown origin are available elsewhere.

 

And TinIndian is absolutely correct on the Teflon (either paste or tape). I once thought I had finally found a legitimate use for Teflon tape. My Dad always loved to mow the yard. We have about 4 acres, and I had planted over 150 various walnut, pecan, and pawpaw trees. As Dad got older, his eyesight was not as good as it had been, so I purchased some brightly colored Teflon tape and tied it to the wire surrounds that I had placed around the trees. All was well until the deer ate the tape! Ended up painting the surrounds. Hope they have John Deere mowers in heaven!

 

Jon.

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  • 2 weeks later...

After getting the car today, I spent some time trying to make it run smoothly...@^!#. I got the choke so that it would not close under acceleration when hot, and it seemed to run well... Then after revving the engine up some, it would be smooth only for a short while and then get lumpy and run rough... The 42 manual on the Stromberg AAV carb http://www.oldcarmanualproject.com/manuals/Buick/1942/Shop Manual/07 Engine/image51.html is not the clearest regarding the choke adjustment or set up when cold/hold... If anyone can explain this in layman's terms it would be appreciated... I will probably attempt to take the carburetor apart tomorrow, but I'm afraid again, of not having any special tools and get stuck in the process... I have a kit for Daytona Carburetors (#2001) but I'm rolling the dice since I ordered prior to getting the car. Still to figure out carburetor #. If anyone knows a good rebuilder or has any useful hints or tips for this model carburetor it would be appreciated... Thank you.

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Philip - the carburetor number is 7-57.

 

To adjust the choke (assuming that the carburetor is in good condition, and only the choke needs adjusting);

 

(1) Wait until the ambient temperature is between 65 and 70 degrees F.

(2) Remove the air cleaner

(3) Loosen the gland nut securing the heat tube to the choke cap

(4) Loosen the three retaining screws that, with the little triangular retainers,  secure the heat cap.

(5) With one hand, grasp the throttle arm, and rotate the throttle to wide open, then back it up to approximately half open.

(6) With your other hand, rotate the choke cap in the direction that allows the choke butterfly to drop open, then reverse direction and rotate until the choke JUST TOUCHES CLOSED!

(7) With your third hand, snug the three retaining screws.

(8) Snug the gland nut securing the choke hot air tube

(9) Replace the air cleaner.

(10) Go play.

 

http://www.thecarburetorshop.com/Automaticchokes.htm

 

After driving for 20 minutes or so, remove the air cleaner, and you should see the choke butterfly is vertical. If not, you have other issues.

 

Jon.

Edited by carbking (see edit history)
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Why do you think the carb is the problem?

 

How does the fuel pump work?

Does it have a good spark?  Advance/retard working?

 

Is the flap in the exhaust manifold operable?

Free to move?

What position is it in with engine hot & cold?
 

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Edited by 1939_Buick (see edit history)
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27 minutes ago, carbking said:

(7) With your third hand, snug the three retaining screws.

 

Sure -- but then how am I supposed to scratch that annoying itch...?  :huh:

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3 hours ago, EmTee said:

 

Sure -- but then how am I supposed to scratch that annoying itch...?  :huh:

Fourth hand...if you've got three, there's surely another hanging around likely getting into trouble. 

 

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Hello Jon,

 

Thank you very much for the detailed instructions regarding the choke... I just went to the garage and started the car right up. As I rev the engine up after a few minutes idling, it seems to run a little better than yesterday, but I noticed the choke is still off. While moving it yesterday (actually got it not to close while the engine is hot) I noticed that the 3 screws holding the choke cap were loose and they allowed me to move the choke spring freely... I also just checked the tube and gland nut (which is tight) but the tube moves freely which tells me a spacer/gasket is missing?

 

And to answer 39 Buick,  I think the carb is the problem since the previous owner has been fiddling with it; just to give you an idea, the idle mixture screws were about 5-1/2 turns out and the choke would close when you throttle up with the engine hot... As for spark or timing, I looked at the cap, rotor, and points and seemed OK. I say seem Ok since the car fires right up (I know should do a tune-up) but has had a rough idle or intermittent rough idle.. As you rev the engine up and down, sometimes it is smooth afterward and sometimes lumpy, bringing me to the vacuum advance question... I do not know how to check it yet..:(

 

Continuing, the fuel pump is at least 10 years old, but have not closely inspected... The exhaust flap moves freely, I will have to take photos of the cold and hot position... I need to make sure the bimetal spring is installed correctly on the manifold otherwise the flap would just sit there and bounce... There is also a second smaller tension spring in the intake manifold under the carburetor (remember it is a 47 engine) that is free and can be rotated around...

 

Back to the carburetor, I have a question as to the thickness of the spacer and position of gasket...Is the order of assembly spacer, gasket, carburetor? How thick is the spacer supposed to be?  Thank you.

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I just discovered that the bimetal spring on the l/h side of the exhaust manifold is not locked in the post...It will be fun to remove the frozen screw that holds a small shield in place!. There is also an (anti-rattle?) spring missing on the right side of the manifold... I may be contributing to my poor running condition. 

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Here are some photos of the problem.. The bimetal spring (left) may be facing the wrong direction and flipped over... The supporting post in on the other side. Next, the anti-rattle spring is missing, where does it attach to exactly? I also have a fitting into the manifold that I 'd like to eliminate since it serves no purpose as far as I know... Thank you.

 

 

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I took the carburetor apart today, only without being able to get to the piston pump assembly... It did not offer any resistance while removing the upper cover. As for my previous question regarding the spacer/base or lower gasket, this is what was removed which does not seem correct... It was not pristine inside I must say. Jets had some damage to the slot surfaces and imagine they may be worn inside after 80 years since they do not come with any carburetor kit. If anyone has a (NOS) 7-57 model available I would consider if not cost prohibitive... Old gas and dirt along with the other manifold issues already mentioned may be the cause of the poor running condition/backfire-sputtering and intermittent rough idle... We will see after I restart. I have to source out a vacuum advance tube tomorrow if possible, since the fitting going into the carburetor was completely stripped out. 

 

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Hopefully these photos will help you understand how the manifold valve connects and operates. The fitting in your manifold is wrong. It is supposed to be a right angle fitting to which is attached a copper tube which is used to drain excess fuel down to the ground to prevent it from landing on a hot exhaust manifold or hot exhaust pipe. I don't have a good photo since I loaned the pipe to a friend to copy since his car is missing the pipe. I am attaching photos of that taken before restoration.

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Hello Mathew,

 

Thank you very much for the photos, they help quite a bit. I was going to just plug the manifold, but I am glad you saved me from trouble by letting me know it is a drain for excess fuel.. It may have been a disaster. As for my other concerns, It looks like there is a small bracket attached to the manifold that would hold the other end of the anti-rattle spring? Hard to tell.. As for the heat riser spring on the left, I was able to remove a small lock on the shaft and turn the spring to the correct position so it rests on the small post. A small victory in my mind towards getting the car to run better...

 

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Here's a photo of the tube for my 1939 Roadmaster.  My car has a plug in the hole on the intake manifold.  I bought this one from Dave T in Minnesota.  I planned to install it, but didn't for three reasons. 

 

1) My engine, come to find out, is not original.  It probably dates from 1946 or 1947;

2) I don't experience flooding issues;

3) My mechanic tested the piece and it doesn't seal on vacuum, which is what it should do once the engine fires up. (The ball bearing must be dirty or corroded.) 

I also have a good spin when I start the engine, even in hot weather, because I upsized the radiator after the water pump failed and threw the fan into my old radiator.

The tube is now a curiosity piece in my garage. 

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Hello Bob,

 

We have much in common, for I have a 47 engine in my 38 Century also.. I will be more than happy to clean your garage...;) I installed this temporarily until I can source out the correct one..

 

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I hate to revisit a topic, but after getting the carburetor rebuilt plus points, plugs, cap, and new vacuum line the car runs much better, except I still do not have the manifold/heat riser flap fully adjusted or operational... It seems that the manifold lever that the anti-rattle spring is attached is bent, and if attached to that position there is too much tension on the spring for the flap to move anywhere... Again, I may have positioned the clip for the anti-rattle spring in the only logical place in the manifold which does not seem to work, therefore:

 

1- Can anyone confirm the correct place to anchor the anti-rattle spring

 

2- Confirm if the side plate welded to the inner flap is bent

 

3- Confirm the position of the counterweight when cold (All the way down) and hot all the way up (at least 3/4 of the way up) 

 

Unfortunately,  the illustrations in the 42 manual are not clear enough in this respect...They do not offer a comparison of the position of the flap inside and outside. 

 

Thank you

 

 

 

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The bracket for the spring attaches to the bolt just below the flapper valve, shown in your photos just below the valve (where the exhaust pipe attaches to the exhaust manifold). It is shown in the diagram on page 6-42 of the 1938 Service Manual.

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Thank you, Mathew, I just rectified that yet still the spring obtained from Bob's Automobilia is very strong to allow the flapper valve to move anywhere... I found a second softer spring and that still is also too heavy to allow anything to happen. In conclusion, and looking at the diagrams regarding the valve:

 

1- With the weight down the heat is allowed into the upper portion of the exhaust/intake manifold to aid in warm up.

 

2- As the engine warms up the weight should move upwards and allow most of the gasses to go down towards the exhaust pipe...

 

If I am correct, the thermostatic spring needs to be replaced or adjusted... The way it is now and in order for the car to run smoothly, I have to manually help the weight upwards about 1/2 to 3/4 of the way for the car to run well... Once it is there, it stays but it is not moving too fast on its own. I would have waited longer, but coincidently, after cleaning the debris out of the fuel pump bowl, I discovered fuel spraying out of a vent hole in the pump... I imagine that is the warning sign to replace? Other than that, it runs much better than day one!..:)

 

 

 

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The Spring is quite stiff. If your spring looks like the one in Gary's photo, it is correct. I have never paid much attention to the valve in my 1937 Century but the car runs well. As I am putting my 1938 Century back together,  I will check it out a bit more. With modern fuels, you could easily position the valve in the "hot" position and ignore it. The car might be a bit cold natured for a minute or so after start up, but it would run fine. I suspect if you are having some issues upon start up, it is probably related to the choke operation more so than the exhaust butterfly valve. 

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Yes, the spring is just like the one from Gary's photo and seems incredibly stiff, so I tried a different one and still did not seem to work... The choke seems to be working now, but It is more of a rough running problem when the engine is warm unless I manually move the counterweight half way up at least and then it will smooth out...

 

Interestingly, if you look at my counterweight in the cold position it is resting down. If yours is in the cold position it is facing upwards, the opposite of mine... I just figured ot that I have a 1939-1953 exhaust manifold valve body (Oldbuickparts.com)... Would the counterweight be set up differently for the later years?

Unless someone welded the flap in the wrong position, to begin with then the anti-rattle spring set up will not work at all...

 

I am tempted to remove the downpipe to see how exactly the flap is resting in its current position. What a pain this has turned out to be. I really dislike the wrong parts, nothing but trouble @$%!!

 

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Edited by philipj (see edit history)
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Speaking in general terms (since I don't have a Buick the correct year to look at), it looks all wrong.

 

The general plan is that the weight should be sticking UP in the cold position. As the thermostatic spring relaxes with heat, the weight should fall in such a way that the heat riser is bypassed. On most cars this is about 90 degrees of movement, usually slightly less on an inline engine like this one. In the bypass (HOT) mode, on most cars, the weight will be pointing at the engine block more or less.

 

Anti rattle spring arrangements vary, but probably the heat riser, when open, "rides" on the stiff spring as a lower stop, to keep the plate from rattling as you go over bumps. It could also be an "over center" arrangement so that it acts as a "stop" at both the open and closed position.

 

Find out what that weight is doing in relation to the plate. It sure looks wrong to me. I suspect it should not be possible for the weight to be pointing straight down.

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Houston we have confirmation of a big problem! Despite the fact that the bypass valve does not seem too old, the plate inside has come loose and moves almost freely, but sometimes gets stuck in the shaft... That explains why the car would be very smooth an sometimes rough when hot. The plate was moving all around...

So with the heat off (cold) the lower portion of the plate should be resting against the outside, in other words, facing me and the weight should be up?

 

Another question, can I remove this component without dismantling the entire exhaust manifold?

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I don't recall how it all bolts together but I think you are about to take it all apart. If you can get to the point where you can see the valve, you should be able to see where the original tack welds held it onto the shaft. Simply retack it in the original position and you should be fine. I think the confusing part is how the manual refers to the cold/hot condition. With "heat off" the weight should be a little less than 1/4 turn clockwise from vertical and the valve should be as shown in the service manual. Here are a couple of photos of the diagrams from the service manual.  "Heat off" as I understand it, is referring to when the engine is Hot, and no additional heat is needed to heat up the incoming intake air. "Heat on" refers to when the engine is cold and the intake air is designed to be heated. 

 

To summarize, when the engine is cold, the weight should be nearly vertical and the valve should be diverting exhaust to the intake manifold. When the engine is hot, the weight should be turned not quite 1/4 turn clockwise from the vertical position and the flapper valve should be turned to divert the exhaust straight down and out to the exhaust system. 

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Are any of the gaskets leaking? If not is sort of looks to me like you could get away with removing the heat riser separately.

 

Usually with a setup like that you would assemble it, and the intake and the exhaust to the head all at the same time, tightening all of it slowly in a sequence so that everything pulls into place properly.

 

It seems to me, from the pictures, that if it is assembled correctly now, and not leaking, you should just be able to remove the riser and then put it back (you'll need gaskets) after fixing it. If someone knows different, hopefully they will speak up.

Edited by Bloo (see edit history)
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Well, good news and good news... I was able to remove the exhaust manifold valve body without any major mishap to confirm a loose plate. It id does not ever appear to have been welded to the stainless steel shaft, but I think that the two cotter pins that kept the shaft from moving lateraly were somehow partially holding this plate in place, and as they rusted out the plate started to move...

Following are three shots of the valve with the spring and weight in the resting position with the plate in various places.. By the way, with the thermostat spring in the resting position is sitting on the small post, and the weight is pointing downwards... In this position, I need to know where the plate should be to secure it...

 

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Edited by philipj (see edit history)
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