I've been dealing in Autolite 4100's quite a bit. They are a good hardy carb, and the annular fuel discharge is highly touted and revered as 'hillbilly fuel injection.'

But! This is a 40+ year old carb. Prices have gone up quite a bit because of Pony Carbs and restorers looking for original numbers to go on their mustangs. As always, questionable business practices follow money. By that I mean rebuilders have are attracted by the profit margin, and parts are getting swapped without regard for intended use of the carb. Big block carbs are being rebuilt with small block boosters. Carbs made for auto trans are having throttle shafts changed to one from a manual trans.

And people wonder why they are difficult to tune. Even when the seller lists the serial number from Ford, still, boosters are not original, etc., making the carb some wierd, untunable hybrid.

Recently I bought one on ebay. It sat in garage for months before I broke it down. When I did, I noticed the butterflies didn't seem to close properly. Upon closer examination, I could see the edges were not angled. The butterflies were home made, and my warranty was long dead.

Buyer beware. Holley and Edelbrock are still making new carbs, thank goodness.

 

yeah...
the one i got off Ebay was good, but i won't tell you how much i had to pay for it.

another reason to consider the Summit carb...

 

Good to know. They seem like a great carb, but with the price and how difficult it seems to find a good one, I think I'll forgo the effort. That's too bad if that's what they've come to.

 

i like to buy carbs at swap meets. i get to judge how much i think they have been tinkered with . Also, i can check for frozen shafts, loose shafts, even open them up and look inside, plus no shipping, etc...jack

 

You're right, it's always better to have the carb in front of you and check it. But the 4100, the smaller 465 cfm, is hard to find and usually not seen at the swapmeets I've been to, but...

I bought one on ebay to get a ford kickdown. What I've found wrong with this carb is amusing. The butterflies were on backward, the beveled edge wrong so they didn't seal correctly. Then I found two of them had holes in them where, I assume, the owner had pounded them with a screw driver to free up a frozen shaft. The shaft was bent too. So, I had to decide how to proceed without spending money. I refused to buy another carb to make this one workable. They aren't cheap.

So, I had an old 600 cfm, and I started thinking. I took the butterflies out and the primary shaft. I was happy to find the 600 cfm shaft worked on the smaller 480 cfm. I also installed bronze bushings on the primary shaft. But then I needed the butterflies, and could'nt find or steal them anywhere.

So...I took the larger butterflies and decided to cut them down to fit the 480 cfm. I put the larger and smaller butterflies together, bolted them together, and cut the larger down, and beveled them by hand with a file. I'm also thinking of filling the voids with bondo to prevent v. leaks. All good fun.

 

All good adaption and improvisation

 

I'll post some pix tomorrow. On my carb there are two very fine vacuum lines coming off the airhorn. One goes into the primary boosters and the other into the s. boosters. They activate the secondary air diaphram that opens the secondary butterflies. The previous owner (ebay) clamped the secondary v.lines closed, so I heated up the airhorn with a torch, pulled the clamped one out, and changed it with the one from the donor carb. A little loktite and it was good.

Also, due to my Quadrajet experience, I had to enlarge the vacuum edifice to help the secondaries open. If it is too much, opens too soon, then I thought I could slightly pinch the tube to compensate.

So, I started with .048 on the primaries, and .067 on the secondaries. I know the secondaries are way too large. I'll probably drop down the .052 on the secondaries, and right about .046 on the primaries. We'll see.

 

So, I posted this to warn people about what 4100's are being sold on ebay. I paid iirc, $110 for this carb. Then the seller refunded me $40 because I noticed a vacuum tube that had been clamped shut.

It was not as difficult as I thought it would be to fashion a new butterfly.





Above is the new secondary butterfly on the right. I may have to take them out again since the shaft does not contact the adjustment screw on the side of the carb, and that tells me they are not allowing the shaft to pivot as much as it is supposed to.

I had a problem with the 4100 before. Fuel was oozing past the needle/seats no matter where I set the float level. I thought it might be because I didn't use the oem filter that screws into the front of the carb. I just didn't have space for it. I use a DP intake and the filter would have hit my valve cover. At one point I suspected the oem filter may act as a psi reducer/regulator. But when I examined one, I could look right through it. So, I went with a fuel pressure regulator that I could adjust from 1-4 psi. My pump was putting out 4 psi.

I originally bought a Specter, but found it to be plastic, with plastic hose fittings. Plastic for $24.99! I didn't want it to explode some day, so I found Mr. Gasket made the same regulator, all metal, with brass fittings, for $31.





I also bought new jets from All State carbs. I would say to stay away from Mike's Carburetor's jets. The inlet is not beveled, and on the ones I got I could see a burr at the fuel entrance. Metal fragments in carbs are not a good thing.



I think I'll use this oem heated spacer, in conjunction with the manifold heating plate I have under the intake. I was thinking of cutting off the hose fittings, and tapping each side to fit a 90* fitting for the hoses. With my headers right under the carb/intake the carb gets very hot.

I'm also planning on using this heat shield.

 

Thanks for the photos!

 

In case you need it or don't already have a copy, here's a link to the factory 4100 service manual:

Classic Inlines - Autolite 4100 Service Manual

 

BVA: Thanks for the link.

Does anyone know how to read the numbers/letters on the Holley/Autolite power valve?

They all are stamped at four places, as though at the position of 10, 2, 4, 8 o'clock. I just use the one in the kit, but would like to know how to read them in case I want to change just the p.v. Thanks.

I bought a reamer on ebay when I did the throttle shaft bushings. They, this type, is very interesting. Imagine a rotary file with about 4" of cutting surface and 7-8 inches of shaft the diameter of your existing throttle shaft. You put the CUTTING END into the drill chuck and run it in reverse. The shaft rides in the carb where the t. shaft goes, so you drill correctly. I paid $50 from Carb Junky's, and I could not get it to cut! I called and confirmed I was doing it right. But it would not cut. Again, beware.

 

f-250...i just got done modifying my heat plate like the one you have pictured above. the way the jacket is molded internally...it makes a pretty sharp bend inside the plate just past the fitting i, and soon to be you, cut off. i ended up slicing some material off of the plate itself, from the corner to have a more perpendicular surface to tap into for plumbing. just take a pencil or something and slide it into the current fitting, you'll see what i mean.

 

Thanks, Dude, I'll take that into consideration.

I'm going to be using one of the plates I make on the bottom of the DP, and the one pictured above between the carb and manifold. I've never seen anyone use both, but I need a spacer for clearance anyway, so I thought I'd hook them both up. On a v8 the carb sits atop a manifold with cooling ports running through it. It's something else for me to tinker with. I'll see if there is any difference.

[B]Holley and Autolite power valve:[B] On the valves, in the position of 10, 2, 4, and 8 o'clock, there are letters and numbers. Does anyone know how to read them? Thanks.

 

I found out how to read the Holley power valves. They also are used in the Autolite 4100. On the flat face you'll see four letters numbers stamped in the positions of 10, 2, 4, and 8 o'clock. It is the numbers on the right side that tell us the vacuum rating. Just imagine a decimal point between the two, and read the one on top first.

To determine which valve to use, take a vacuum reading of your engine at running temperature, in gear. Take that reading and half it. If your engine idles at 16, and you half that, you end needing a power valve rated at 8. But they only come in uneven numbers, like 7.5, 6.5, 5.5, etc., so drop down one notch, and get a p.v. with a 7.5 rating.

AUTOLITE 4100 PARTS: After digging around online for quite a while I have found sources for nearly all 4100 parts. Start on ebay. Several retailers operate 'stores' there, but if you search around and find their source you'll buy them less expensively. [B]Carburetors Unlimited [B] has quite a few parts. Mike's Carburetors is another source. There is also AllState Carburetors for very inexpensive jets. The last place, CJ Pony Parts[B] has the base spacer with vacuum, and the choke heat shield, not to mention the air cleaner stud.

Helpful notes: The throttle shaft of the larger 600 cfm (1.12) is interchangable into the smaller 480 cfm (1.08).

The larger 600 cfm is less expensive and easier to find. It is possible to take the butterfly plates from a 600 and cut them down to fit the 480.

The new style synthetic floats get lazy. I always replace them with $12 brass ones.

Holley power valves are a direct screw in fit, and Holley parts are cheap and plentiful.

Some rebuild kits don't come with the secondary vacuum diaphragm, and when you go to buy it separately they charge an extra $20, so check if it is in your kit before hand.

These carbs don't like much fuel psi. I use a Mr. Gasket regulator to lower the fuel psi to 1psi. Otherwise fuel oozes past the needle/seat.

These carbs have a thin side wall on the throttle plate--the area that mates with the intake manifold. Therefore I like to use the oem spacer that the Gods at Ford used. I'm also a fanatic about cleaning ALL surfaces of ALL gasket residue. Not doing so may cause a vacuum leak and will keep you running around the carb tweaking and tuning for untold hours--to no avail.

Check the bottom for true and resurface if needed.

You can fill the primary bowl with mineral spirits and and test the accelerator pump with the top off. Move the arm, with the primary booster, weight and ball and screw and gaskets in place, and you should see fluid oozing out into bore.

Good luck.k

 

Oh boy After all that work I try out the carb and can't get it to idle under 2k. So I ck for v.leaks and ck everything else. Pull the carb and am looking it over closely to make sure the mix orifices are below the throttle plates, when heck, I notice air bleeds drilled into each primary bore, into the booster fuel channel. I think the fuel channels themselves have been bored too. They are larger in diameter than those on my 600 cfm.

At that point I realized the carb was crap and that I had wasted a lot of $ and work to try and make it work. Women and carbs, boy can I pick 'em.