Torque Specifications

Here are the torque specifications for your 65/66 car. At the bottom is the general guide for bolts of various sizes. One should always proceed with caution when dealing with 40+ year old components. This will not be their first rodeo. You have decades worth of metal fatigue due to wide variations in temperature, along with the simple march of time, slightly distorted threads from previous repairs, slightly looser threads from the metal loss due to rust, etc.. to contend with. And, metalurgy in the 60s wasn't anything close to what it is today. There was a much greater degree of variation in the strength and consistency of the seemingly identical components. By now, each and every component has it's own distinctly unique set of characteristics. You will need to be much more cautious and pay a lot more attention to what you're doing than you would if you were just slapping together brand new stuff.

VIN decoder for 1965 and 1966 Mustangs

I just realized that I haven't gotten around to putting this up yet. Oh, well.Here's what the VIN on your 65/66 car means.
The first digit is the year model, as in 5 means 1965 and 6 means 1966

The second digit is the code for the plant at which your car was built. F is Dearborn, MI, R is San Jose, CA and T is Metuchan, NJ. Those were the only three plants that were building Mustangs then.

The third and fourth digits represent the body style. 07 is a coupe, 08 is a convertible and 09 is a fastback.

The fifth digit is the engine code.
U is a 170 cid six cylinder with a 1 bbl carb
T is a 200 cid six cylinder with a 1 bbl carb
F is 260 cid V8 with a 2 bbl carb
C is a 289 cid V8 with a 2bbl carb
D is a 289 cid V8 with a 480 cfm 4 bbl carb
A is a 289 cid V8 with a 480 cfm 4 bbl carb
K is a 289 cid V8 with a 600 cfm 4 bbl carb ( along with some other cool stuff)

The last six digits are the sequential production, or 'serial' number.

The picture indicates the location of the three VIN stampings on a 65/66 car. If you open the hood, you should be able to see the front one on the driver's side. To see the other two you have to remove the fenders.

How much is my 65/66 Mustang worth?

A question that is frequently asked is ' I have a 65 Mustang. How much is it worth?', and then the process of trying to coax a little more information out of the person begins, which often seems like pulling teeth. The simple truth of the matter is this. There is absolutely no way to accurately appraise the value of a forty+ year old vehicle based on a couple of emails and a phone conversation. The market variables are sometimes far too subtle and complicated for someone to stick a price tag on the car based on such vague information. The statement of ' I have a 65 Mustang' does not narrow it down at all. There is a world of difference between a rust-bucket 6 cyl coupe, a 98 pt. trailered concours factory GT K code convertible, and an R model GT-350. There are a few things that are the kiss of death for a 65/66 Mustang's value.



The motor that the car came with originally is what the car is. What is physically present in the car at the moment means almost nothing. If your car came originally with a 6 cyl, you have a 6 cyl car. " But it now has a supercharged 427 SOHC motor in it." You have a 6 cyl car that has a very expensive motor in it, and that motor would be worth even more if it didn't have that pesky 6 cyl Mustang wrapped around it. The car is actually bringing down the value of the motor. Here is how that heirarchy works. The fifth digit of the vin tells you what motor/carb the car came with originally. The value, from top to bottom, would be K, A, D, C, F, T, U, with the K code at the top of the list and the humble U code as the low man on the totem pole.



The body style matters. With everything else being equal, a fastback is worth more than a convertible, and they are both worth more than a coupe. People like the fastbacks, and Ford built about 5 times as many coupes as they did fastbacks, so, rarity+desireability= more expensive. Same deal with convertibles. People like convertibles, Ford didn't build very many compared to the coupes, and a convertible is far more prone to rusting away to nothing, so more of them are lost or parted out every year. The totem pole of body styles would be fastback, convertible then coupe.

Then there is the condition of the body. Each and every car is in it's own unique condition. Many of these cars have been wrecked, some on more than one occassion, with the following repairs being done with various levels of skill and quality. Sometimes the repairs were done very well, but the method is slip-shod by it's very nature. A car gets hit real hard in the rear. Rather than do all of the work needed to fix what's there, it was not uncommon to just take another car that had crashed into something, crushing the front of it, saw both cars in half and weld the two good ends together. This is called being 'clipped', and you have to get underneath the car to see if this has been done. There is not supposed to be a raggedy seam going all the way across the middle of the car. A car can be drop-dead gorgeous in pictures, but have the entire cowl area or the rear frame rails be rotten from rust, rendering the car unsafe to drive. You have to look at the car very carefully and know exactly what's supposed to be there.

And then there is always the question of whether or not the car that you are looking at really is who it says it is, especially on the K codes or the factory GTs. On the K codes, there is a little more to it than looking at the breather decal. The K codes came with a manual choke carburetor. This manual choke has a cable going from under the dash inside the car through the firewall and out to the carb. That cable went through a specific hole in a specific location and was of a specific size. The K codes were the only cars to have this. If that hole isn't in the firewall, something is very seriously wrong here, even though the vin is that of a K code. All K codes came with a 9 inch rear end and all other 65/66 Mustangs came with either an 8 inch or the integral carrier of the 6cyl cars. On a 9 inch rear end the snubber is mounted to a bracket that is attached to the rear end. All other 65/66 Mustangs have the snubber bolted to a piece that's spot welded to the floor of the car. That bracket should not be on the floor of the K code. To make things more interesting, there is a piece welded to the floor of the K code also, for the snubber to bump into instead of just sheet metal, and it is virtually impossible to describe them both in such a way for someone to be able to accurately identify what's on the car that they are looking at. The differences are very easy to tell if you know what the K code bumper plate looks like, though. If the car has the snubber mounting bracket instead of the bumper plate, again, we have a big problem.
A person could say that 'This K code has it's original, vin stamped motor' and technically be telling the truth, but the motor is missing nearly eight thousand dollars worth of parts, like the carb, fan, balancer, distributor, main bearing caps, etc... The 65 K codes had a unique set of motor mounts that don't look anything like the other 65 Mustang motor mounts, and they are very difficult to find, and extremely expensive when you do finally track down a set. And, just for fun, Ford made them very, very similar to the Fairlane motor mounts, but not identical, but it is extremely difficult to tell the K code mounts from the Fairlane mounts when they are bolted to the car, especially if they are all funky-looking and covered with dirt and grease and stuff.
The bottom line is that, in order to accurately determine the fair market value of a 65/66 Mustang, someone that is thoroughly familiar with 65/66 Mustangs is going to have to have a look at the car in person. When someone asks me what a car is worth that I have never seen and don't know anyone that has, the only thing I can do is ask them to email the car to me and let have a look at it.

On a high dollar car, like a K code or a GT, there is no way to tell what a particular car is worth without having someone that knows exactly what to look for go and inspect the car in person.

Why we call them 64 1/2 Mustangs

There has always been some discussion about this point among Mustang folks. The reason that there has always been discussion is because the point is a little more complicated than it might seem at a glance.On the one hand, you have the fact that all Mustangs built prior to the 66 model year have 1965 vins, and on the title it says 1965 Ford Mustang.One would think that this would pretty much exhaust the matter. But, on the other hand, you have a mountain of evidence to the contrary.First off, you have dozens, if not hundreds, of parts on a 65/66 Mustang carrying a part number that goes C4Z something or another. If you check with your handy Ford part number decoder you will see that C4Z means 1964 Mustang. Fortunately, I have a pretty extensive collection of original Ford publications from that era. The first picture is the cover of a Ford publication that they put out in aug of 1963 in preparation for the 64 model year. It is not a copy or a reprodution, it is a 44 year old, original brochure of about 16 pages. On the cover you see several 64 model cars with license plates that say '1964'. On the top is a Mustang, but they have it turned sideways. The next couple of pictures are of a trim and upholstery guide. Each Ford dealership was given a couple of these every year in preparation for the new model year to help people see what their new car would look like with a particular trim, upholstery and paint scheme. And in it we have the Mustang section. You will also notice the absence of the fastback body style. Those were not available during the 64 model year, but the coupe and convertible were, even though this car that was built in march or april of 64 had a 65 title. Clearly, Ford was building and selling Mustangs during the 64 model year and these cars have numerous distinct differences from the cars built and sold for the regular 65 model year, and the differences between a 64 1/2 and a 65 are far more numerous and significant than the differences between a 65 and a 66. That's why folks keep arguing about it. There is no clear-cut right or wrong answer. It just depends on how heavily you weight 'this' aginst 'that'.

Since I was 8 or 9 I have been wondering about why Ford gave the Mustangs that we call 64 1/2s 65 VINs. They started building them in like feb. of 64. There isn't a single part anywhere on the car with a 65 part number. If you see a part with the number starting out C5Z and going on, that part has been replaced. Ford quit using 5-bolt, generator charged motors at the end of the 64 model year. All 65s had 6-bolt, alternator charged motors, etc... Everything about the cars say that they are 64 model cars, with the exception of the VIN. Why did they do that? Someone had to make that decision, and the decision was made before they ever built the first Mustang. What was the rationale behind it? They started out by building about 25,000 Mustangs to start selling on April 17 of 64. They felt like that would be enough to carry them through until the 65 model year began. However, they sold every one of those cars, plus took orders for about 15,000 more on the april 17 of 64. They also introduced several other pretty cool things in 64, like the factory lightweight T-bolts and some K code Falcons and stuff to hedge their bet on the Mustangs. They had no idea if these cars would sell or not, and just in case they still had 20,000 of those first 25,000 Mustangs in aug. of 64, they could still sell them as brand new 65 model cars. They didn't know. Maybe those Mustangs will do the same thing that some other seemingly good ideas on car design did, namely, they couldn't give them away. They didn't do it to confuse and bewilder as yet unborn enthusiasts at all. It was one more way to hedge the bet.

I have actually pondered this question on a regular basis and have come up with nothing for a really long time. It just made no sense to me. Everything about it is a 1964 model car, and yet, someone made the decision to title these things as 65 model cars in the winter of 63/64, They weren't building any other 65 model cars. They weren't even making any parts for 65 model cars yet. They were advertising them right beside other 64 model cars. It was a very strange decision to make. It would probably have never even crossed my mind to do that, unless I was sitting in a meeting discussing this and someone said, " You know, we're all going to be looking for jobs if these things don't sell" Then we would start brainstorming about how to avoid that very unattractive eventuality, and that's where the idea for 65 VINs came up. For as far back as I can remember, I would just sit down and think about something that pertained to a 65/66 Mustang on a regular basis. Sometimes I put my car up on jackstands and crawl around underneath it, just looking at stuff. Like watching television. For hours.This 65 VIN thing has confused me to no end for the longest time, and, again, finally coming up with something that makes sense about this, to me anyway, very perplexing question, has made me really happy.

Trunk lock cylinder replacement 1965 1966 Mustang

The first picture shows the trunk latch. Remove the two bolts holding it onto the trunk lid and it will basically fall off into your hand. Make sure that it is, in fact, your hand that it falls into, instead of letting it figure out a way to hit a painted surface.
This is a picture of what you will see when you get the trunk latch out of the way. Remove that nut with a socket wrench and pull the washer off with the nut. That will leave a split, funny looking tube thingy that is pinched onto the back side of the lock cylinder bezel. The split tube thingy will pull off of there.
The next two pictures are the entire assembly. The first is full assembled, minus that pesky trunk lid, and the second is everything disassembled.

This last picture shows the release button for the lock cylinder. You just depress that button with the key in the lock, turn the key a little bit so that the key won't come out of the cylinder when you pull on it, and pull the cylinder out. If the reason that you are replacing the cylinder is that you have no key for it, you can also take a very small flat-bladed screwdriver and get behind the cylinder with it and, with the button depressed, pop the cylinder out like that. The rod sticking out of the back of the bezel is a seperate piece that you will need to put back in before you install the new cylinder, or put your old cylinder back into your new bezel. Whatever it is that you are trying to accomplish here, drop the rod into the bezel, put the lock cylinder into the bezel, making sure that the tab on the end of the lock cylinder is lined up with the slot in the end of the rod, put the trunk lid gasket onto the bezel, put the bezel into hole in the trunk lid, put the split tube thingy onto the bezel from inside the trunk, put the washer and the nut on the bezel and snug up the nut. It doesn't need to be tight enough to have the bezel squash the gasket and crack the paint.


As a side note, if you have accidentally locked your keys in the trunk of the car, ( hey, it happens ) what you do is, on a coupe or a convertible remove the upper part of the back seat and take a half inch socket wrench with about 3 miles of extensions on it, and remove either the two bolts holding the trunk latch to the trunk lid or the two holding the the other part of the trunk latch to the taillight panel area, whichever you can get to the easiest. If you have a fastback, crawl through the trap door and do the same thing. You might have to remove that rear carpeted piece to get the trap door open, depending on how well the trap door is adjusted, which is usually not very well.

Tag codes

When your car was new, it had a bunch of little metal tags hanging on it, some of which might still be on the car today. The purpose of these tags was to tell the people at your local Ford dealership which component this particular car had in it so that they would be able to get the right parts for warranty work. The first tag is what would have been hanging on the front of the carburetor. The C6AF B is which carb this one is. There was an astonishingly large number of different carbs used in the 65/66 model years for different applications on the Mustangs, and I'll put the list of the most common ones down at the bottom. On the bottom row of the tag you see the letter C. That indicates the design change level, which means that the basic design of this particular carb has been modified in some way twice since it's original design. A would indicate the original design, B means the original design has been modified once, C means twice, etc... After that you see 6CC. This is the date on which this particular carb was built, in this case, it is the third week of march in 1966. That goes Y/M/W on a carb tag.
This next picture is of a 65 and a 66 door tag. I whited out the vin to for the privacy of the owners of these two cars, which isn't me. The one on top is a 65 and the one on the bottom is a 66. What this tag tells you is the body style, the body paint color, the interior code, the scheduled production date, the D.S.O., which is the district sales office, or, where your car was sent originally to be sold, the axle code, which tells you the rear end gear ratio, and which transmission your car came with. However, these tags can be purchased brand new from Marti Auto, so, what these tags really tell you is nothing, since there are no original records on the 65/66 cars, and Marti makes the tag with the information that you give him. Fortunately, Marti's tags are a whole lot nicer than Ford's were. The two tags in the picture are original tags. You will notice, for example, that the axle code is not even close to being underneath where it says 'Axle' on the tag and looks a lot more like a 2 digit trans code. Marti's tags have everything lined up real nice and neat, the letters and numbers fit into space a lot better, lots of little differences. On the 66 tag in the picture, it looks like the stuff stamped on the tag is too big for the space allowed. Marti's tags have everything fitting in there very nicely. I think it costs extra to have him make one that's all screwed up like Ford's were.
The next picture is a couple of engine tags. This would have been on the top of the intake manifold, over on the driver's side. The top row tells you the cubic inch displacement of the motor, the plant at which the motor was built, (the lower tag was built in Cleveland, Ohio, the top tag, a 6cyl, doesn't have the build plant on it) the year model of the car that the motor was destined to go into, and the bottom row tells you the date that the motor was actually built, the top one is oct of 65, which is in the 66 model year, and the bottom one is march of 66, also the 66 model year, followed by the engine code number. This number is a lot more important on the V8 cars than it is on the 6cyl cars, because the 289 in the car could have been a plain old, nuthin special C code 289 2bbl or it could have been the high performance 271 hp K code 289 4bbl. A world of difference between those two 289s. Sadly, this tag is the C code.
This next tag, shown below,is what would have been attached to the third member of the rear axle assembly. This tag is actually out of an old Bronco. I'll dig out a Mustang tag and get a picture of it up soon. I put this one here just to show kind of what it looks like. On the Mustang tag there will be a three letter dash one letter code, like WCZ-H for example that tells you the gear ratio, whether it's a 28 or 31 spline,and whether it's a 7 1/4 inch, 8 inch or 9 inch rear end, followed by a number that is the design change level. The bottom row will have the actual gear ratio, which will be something like either 3.00 ( conventional) or 3L00 ( limited slip) followed by a date code which will be Y/M/W and then a plant code, which doesn't really mean much after the warranty has expired, which, on your car, it has.
This next picture is of steering gear box tags. In 65/66 Mustangs there were only three different steering gear boxes used. The top one says HCC-AW on the top. That is a 16:1 steering gear ratio used in cars with power steering. The next one says HCC-AT which is the 19.9:1 steering gear ratio used in manual steering cars, and the bottom one says HCC-AX which is the 16:1 steering gear ratio box that was for manual steering cars that came with the Special Handling Package. All 65/66 K codes should have the HCC-AX steering gear box tag, except for the 64 1/2s, which should have HCC-AX-1, since the Special Handling Package was mandatory for the K codes. Also, the presence of the Special Handling Package does not mean that the car was a factory GT. It was a stand-alone option that could be ordered for the car without the car having the GT stripes, badges, etc.. The bottom row on the tag is the date code which is Y/M/D/ Shift. The bottom tag is Aug 12, 1965, second shift, the middle tag is December 17, 1965, second shift, and the top tag is June 14, 1965, third shift.

1966 Mustang Interior samples and codes

This is material from the original Ford Master Parts catalog for the 66 model year. How this works is you find the interior code for your car in one of the charts ( picture 4 or 5) move over to the right hand side and there will be some numbers representing seats, door panels, etc... If you click on the picture it will enlarge enough for you to actually be able to read it. You then find the patch with that number on one of the other pictures and that's what the headliner or whatever is supposed to look like. Nothing to it.

1965 Mustang Interior samples and codes

This is material from the original Ford Master Parts Catalog for the 65 model year. How this works is, you find the interior code of your car on one of the charts ( picture 3,4, or 5) and out to the left will be some numbers representing the headliner etc.. If you click on the charts or pictures, it will enlarge so that you can actually read what they say. You then find the patch on one of the other pictures with that number beside it, and that's what your seats or whatever are supposed to look like. Nothing to it.

Optional equipment for the Mustang

Here are the available options, along with their part numbers, and how much they would have cost 'back in the day'. These were the prices in June of 1966. You can see slight variations in the prices in different Ford publications printed at different times. The old 'Prices are subject to change without notice' thing.


Television---------------------------------C5AZ-18804-A----------$169.95



Deluxe 14" wheel cover w/spinner---------C6ZZ-1130-B-------------$33.20 (set of 4)


'Mag' wheel cover/14"---------------------C6OZ-1130-J-------------$81.15 (set of 4)


Styled steel wheel-------------------------C5ZZ-1007-B(wheel)------$158.40(set of 4)


Lug nuts----------------------------------C5ZZ-1012-A-------------$9.60(set of 20)


Center cap--------------------------------C5ZZ-1130-G-------------$10.00


Wire wheel cover-------------------------C5OZ-1130-C--------------$83.35(set of 4)


'White wall' trim rings 13"-----------------C5AZ-1211-A--------------$14.58(set of 4)


14"-----------------C5AZ-1211-B---------------"-------------"


15"-----------------C5AZ-1211-C---------------"-------------"


Floor mats/ front twin---------------------C5ZZ-6513086*-----------$7.95


/ Rear twin---------------------C5ZZ-6513106*------------$4.96


*= specify color


Full Tonneau Cover( cockpit cover)--------C5ZZ-76501A42-A(blk)---$52.70


"---------------------------------)--------C5ZZ-76501A42-B(wht)---$52.70

Door edge guards-------------------------C5ZZ-6520910-A----------$3.45

Rear seat armrest with ashtray-----------C5ZZ-6531600------------$15.20 pr (65)

"------------------------------"----------C6ZZ-6531600-------------$15.20 pr (66)

Air conditioner---------------------------C6ZZ-19700-A(6 cyl)-B(V8)-$240.00

Speed control----------------------------C6AZ-9A818-A--------------$71.40

Throttle control kit----------------------C4AZ-9B742-A--------------$10.00

Engine coolant heater------ 550 watt----C3RZ-8B152-A--------------$13.45

"--------------------------"1000 watt--C3RZ-8B152-B--------------$15.50

Both plug into household outlet

Power brakes----------------------------C62A091-A-----------------$47.00

Inside day/night mirror-----------------C6ZZ-17700-A--------------$4.95

Right-hand standard mirror------------C3RZ-17696-A---------------$2.45

Left-hand remote mirror---------------C5ZZ-17696-A---------------$12.95

Cigarette lighter/ map light------------C2RZ-15072-A---------------$3.00

Trunk light----------------------------C2RZ-15A700----------------$2.35

Parking brake warning light----------C4DZ-15A852-A---------------$3.80

Spot light----------------------------C5ZZ-15313-A(L.H.)-----------$29.95

"---------"--------------------------C5ZZ-15313-B(R.H.)------------$29.95

Turn signal-Fender mount----------C5AZ-13A310-A----------------$7.15 pr

Compass----------------------------C4RZ-19A548-A----------------$7.95

Trunk mount luggage rack----------C5ZZ-6555100-F---------------$39.95

Luggage rack hold-down straps-----C5ZZ-6555196-A---------------$5.25

Electric clock-----------------------C6ZZ-15A000-A----------------$20.80

Vinyl top--------------------------C5ZZ-6350005-A(blk)-B (wht)--$69.50

Stainless sill plate-----------------C5ZZ-6513242-A----------------$9.95 pr

Litter basket---------------------C1AZ-19D504-A thru D----------$2.45

Tissue dispenser------------------C3RZ-19A549-A----------------$3.95

Remote trunk release-------------C6AZ-65432A00-A------------$6.95

Adjustable clothes rod-----------C4AZ-19D536-A-----------------$3.00

Auto vacuum (plugs into lighter socket) C5AZ-19E521-A----------$14.95

Radiator bug screen-------------C5AZ-8198-A-------------------$1.95

Am/Fm radio-------------------C6ZZ-18805-BA----------------$123.15

CB radio------------------------C5AZ-18805-E------------------$179.50

Two-way walkie-talkie---------C5AZ-18805-F------------------$119.50

Studiosonic sound (reverb)-----C6AZ-18875-A------------------$27.95

Luggage rack zipper bag-------B9AZ-19B507-B-----------------$39.95

Rotunda child car seat---------C6AZ-19E535-A-----------------$29.95

Rotunda child safety vest------C6AZ-19F519-A-----------------$10.95

Child proof lock knobs--------C6AZ-5421850-A-----------------$2.95 pr

Reflector/ flare kit-----------C5AZ-19E500-A-------------------$11.20

Fire extinguisher/ 2 3/4 lb--C3RZ-19B540-A-------------------$16.50

"-----------------" 5 lb------C5AZ-19B540-A------------------$27.50

Dual air horns---------------C5AZ-13800-A-------------------$53.50

Glove box lock--------------C4DZ-6206081-A-----------------$2.50

Engine gauge kit------------C6AZ-10B944-B-------------------$45.00 ( A single round gauge housing with engine vacuum, water temp, oil pressure and volts. Not the rally-pac)

Cobra Tach------------------C5AZ-17A326-A (6K, V8) (-B 6k, 6 cyl) $42.50

Cobra tach------------------C5AZ-17A326-C ( 9K, V8)---------$46.50

Sun Tach-------------------C4AZ-17368-A (9K V8)-----------$60.00

Sun Tach mounting kit------C4AZ-17368-A-------------------$6.10

Seat belt retractors---------C4AZ-62611A06-A---------------$3.85 pr

I'll put some more of this stuff up later, when I type it up.

Carburetor common repairs and adjustments

This first picture is of the accelerator pump diaphragm housing, held onto the front of the carb with four screws.If fuel seems to be leaking from that hole towards the bottom of it, that means that the diaphragm is ruptured and needs to be replaced. The ruptured diaphragm will also make the car behave very badly coming from a dead stop. First, you remove the four screws and pop the housing cover off and swing it out of the way. What you will see when you do that is shown in the sixth picture. That is the diaphragm itself. Pull that thing off. When you do that, what you will see is in the fifth picture. That spring is what pushes the diaphragm back outafter the arm cam pushes it in. If this is all that you intend to do to the carb, just put the new diaphragm on, making sure that it goes on facing in the same direction as shown in the picture, with the spring underneath it, replace the cover, snug up the screws and you're good to go. Do not overtighten the screws because you could strip out the screw holes and the carb will leak like crazy from that day forth.

If fuel is gushing out of the vent tubes on the top of the carb, that means that your needle and seat assembly is not working correctly. This is commonly called ' float is stuck'. To replace the needle and seat assembly, remove the top of the carburetor by first removing the little clip holding the choke flap arm onto the choke linkage. It is shown (sort of) in the third picture. It is that tiny little clip just to the left of the dirty brown plastic thingy. Next, remove the four screws from the top of the carb, along with the stud that holds the breather assembly wing nut on and remove the top of the carburetor. What you will see is shown in picture #11. In picture #10 you see the float clip popped loose. pop the clip loose on yours and lif the float out of the carb. There will be a little brass thingy with a rubber tip hanging on the end of it, as shown in picture #9. You will then remove the brass seat that is screwed into the carburetor, shown in picture #8. Use a 6 point 3/8 socket wrench for this. When you install the new one, be sure to put the new gasket underneath the seat assembly. Replace the old needle ( brass thingy with rubber tip) , reinstall the float with the needle inside the seat, without dinging it up, reattach the clip holding the float in, and again, you are good to go.

If, when you remove the top of the carburetor, yours is all funky and crusty-looking, like the one shown in picture #7, you need to clean that stuff up before you put the carb back together. Those two brass things that look like screw heads with a hole in the middle of them are your main jets. You remove them with, that's right, you guessed it, a big flat blade screwdriver. That other thing in there with the brass tip is the top side of your power valve. This is replaced by flipping the carb over, assuming that you've emptied the fuel out of the carb by now, and removing the housing cover, as shown in picture #15, by removing the four screws and popping it off of there. What you will see is shown in picture #14. That is the other end of the power valve. It unscrews in the normal way with a 1 inch open-end wrench. Unscrew it and install the new one, again, making sure that you also replace the gasket underneath it, then replace the cover, again, with the new gasket, and that is that.
Autolite carbs, with the exception of the K code 4bbls, have thermostatically actuated chokes. How the choke is adjusted is by loosening the three screws on the choke thermostat housing, which is the round black plastic thing on the passenger side of the carb, shown in picture #3, and rotating it slightly, then tightening up the screws. You will notice that there is an indexing mark on the carb to help you keep track of the adjustments you make. Rotating the housing clockwise makes the choke open sooner, counter-clockwise makes the choke open later.

The idle speed is adjusted by running the screw on the throttle linkage on the driver's side of the carb, as shown on the right hand side of picture #12. The fast(cold) idle speed is adjusted by the screw on the choke linkage over on the passenger side of the carb shown kind of right in the middle of picture #14. Nothing to it.

Basic carburetor function

Here's how your Autolite 2100 or 4100 carburetor does what it does. Understanding this is essential to diagnosing and correcting any problems that it might be having. The carb is responsible for delivering fuel to the engine. How it does this is by a couple of basic physical principles. One is that air moving through an hourglass shaped tube is at it's highest velocity and lowest pressure at the skinny part of the tube. This was discovered by an Italian physist named, that's right, you guessed it, Giovanni Battista Venturi. Your carburetor's fuel bowl has a vent hole on top of it. The pressure at the top of the fuel is normal atmospheric pressure because of the vent hole. The fuel has a few different routes that it can take to get into the venturis, but at the discharge port, the air pressure is lower, because of the venturi effect, than it is at the top of the fuel bowl. That creates a 'push' on the topside of the fuel. An Autolite carb has three basic fuel circuits. One is the idle circuit. This is the path that the fuel follows when the throttle plates at the bottom of the venturis are closed. The discharge ports for the idle circuit are below the throttle plates. This works by straight-up suction, or engine vacuum, so that when the car is at idle speed, fuel is delivered to keep that going. Next is the transition circuit. Here, the discharge ports are slots that are partially below and partially above the throttle plates and works partially by the suction of the engine and partially by the pressure differential of the venturi effect. Last, we have the main fuel circuit, which works entirely by the venturi effect. The discharge nozzles for the main circuit are the ones that are inside the booster venturis, or, the little hourglass tube shaped thingies that you see inside the throat of the carb. The float that is inside the fuel bowl is responsible for keeping the fuel at a certain level. The correct level for the fuel in bowl is slightly below the main discharge nozzles. If the level is too low, the venturi effect won't be strong enough to push the fuel uphill and get it into the carb. If it is too high, gravity will pull the fuel out of the fuel bowl until the two levels are the same, and then the siphon effect takes over and drains the fuel bowl entirely. Where that fuel goes, when the motor isn't running, is straight into your oil pan, degrading the lubricating ability of the oil and making you have to crank on the starter until the fuel bowl is filled up again so that the car can start. You also have an accellerator pump to deliver a little shot of gas to keep the motor running while the carb changes from one circuit to the next. This is also what the power valve does. It is held closed by engine vacuum. As you open the throttle plates on the carb, engine vacuum drops temporarily, allowing the power valve to open and let some more gas into the engine after it has burned the little shot provided by the accellerator pump. The engine vacuum recovers pretty quickly and the power valve closes and the motor is running on the main fuel circuit entirely at high speed cruising speed. Normally the motor is running on a combination of two circuits, depending on what you are asking the car to do, and most round-town driving is down on the transition circuit. Puddles of purely liquid fuel do not burn very efficiently at all. That is why the carb is designed to vaporize the fuel, and you hear people talk about the ' air/fuel mixture'. Inside the carb there are these little thingies called emulsion tubes. These create a mixture of highly airated, but still basically liquid, fuel. When this air fuel emulsion goes out the discharge nozzle, the process of vaporizing the fuel is finished by the shearing and velocity change of the mixture, so that it is vaporized as effectively as possible when it gets into the motor. On the four bbl carbs you have two primary venturis and two secondary venturis. The 4100 has vacuum secondaries. What that means is that the change in engine vacuum caused by hard accelleration or wide open throttle is what causes the secondary venturis to open, allowing even more fuel into the motor, much like a great big power valve. And that is how that works.