Above: It is possible to take these 40+ year old carbs and replate them and make them look like the one above.

If you wonder why people still seek them, it is because they are amazingly simple and supply great performance with their annular fuel discharge--something Holley paid Ford for many years to copy. If you look at the new Summit Carb, you'll see a redesigned 4100.

I wanted to post some things that members dealing with a 4100 might find helpful. First of all, let me mention to be cautious when buying on ebay. I'm finding that dealers are mixing and matching parts. Although the numbers on the carb toe may identify it, the throttle shaft may have been changed, so it no longer has the oem kickdown, or the boosters may have been changed (no one has a chart to show what boosters came oem with any car, carb), throwing all tuning and oem calibrations out the window. Bottom line: If you can find the history of a carb, and buy it from a private owner, not someone who deals in these carbs, you'll be better off.

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.



Above: A bent throttle shaft from an ebay carb. Some times if the butterflies are froze, they use a screw driver and hammer to 'tap' the butterflies, bending the t.shaft.

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



Above: the butterfly on the right was cut down from a larger 600 butterfly to fit the 480 (1.08) bore.

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.



The Mr. Gasket regulator comes with brass fittings, and is, itself, made of metal, not plastic like the cheapo Specter look alike.

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.



Above is the oem spacer I like to use. You can find them on ebay, or at CJ's, which I mention latter on.

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

 

My all time favorite carb. When i was teaching my sons how to rebuild and tune a carb i used a few 4100's. As you really cannot get much simpler in design. with the exception of a predator but i only have one of those and parts are not cheep.

 

Thanks for the info

 

I run the Mr. Gasket FPR too (Eddy's don't like more than 5.5 psi) almost a decade now issue free, as you noted it's much better quality than the Spectre knockoff.

 

Would you have any idea what jet sizes a person should use in a 4100 on a 400ci motor that's stock minus headers?
I just had my headers and a 4 barrel intake installed, but i think my jets are to small...48 primary and 55 secondary.

The stock jets that where in my 2150 2v carb had 56 jets in it.
I have not messed with it a whole lot yet, i need to get my exhaust done first, its to loud to think straight while working on it.

 

So is the 4100 just as simple as the old 2100?

 

Yes these carbs are very simple in design, and easy to rebuild.
I rebuilt both my 2150 2v and now my 4100, very simple and fun.

 

I found an all oem 4100, the 480 cfm model, 1.08 venturi, on a cherry T Bird. It had .047 in the primaries, and .067 in the secondaries. This was on a 390 with the hp package. All State carbs is a good source for jets.

 

The diameter of the booster tubes, the restrictions on their tips, tells you a lot about what engine they were meant for. Also, keep in mind there are two types of 1.08 4100's. There is the small block 480 cfm, and the big block 480 cfm. You can identify the b.b. by running the numbers on mustangtek dot com, or by locating a hole drilled inside the bore of both primaries and secondaries, into the canal that supplies fuel to the boosters. (The copper supply tubes of the boosters sit in this canal.) The hole is an oem air bleed drilled by food to help the carb flow for the b.b.

I also found something very interesting: The 4100 primaries are narrower than the secondaries! With tiny primaries at just slightly larger than one and a sixteeth inch, it gives tremendous vacuum signal and thereby throttle response.

I also found a source for the choke heat shield and the air cleaner stud: cjponyparts dot com.

Note: the holley power valve, rumored to be the same as the autolite, is larger and does not work on the 4100. Use a power valve rated at half your total engine vacuum at idle, in gear.

 

You can get genuine Holley power valves to work, you just have to file down the raised shoulder on the Holley so it doesn't bottom out in the casting. You can also try using the plastic power valve gaskets to help with clearance issues.

Also if you use a Holley power valve in the 4100 you need to open up the casting around it in the fuel bowl to allow for fuel flow as the top of the Holley valve is larger then the original 4100 Ford style.

 

man...now i feel like an idiot for throwing away the old one that came on my 65 t-bird

 

Nice workmanship! I'd like to see the rest of the truck.

 

That's great, but I just don't see why one would go to that trouble when the autolite oem valves are readily available.

 

For those who are running the 4100"s what size jets are you running?
I was thinking about 55 primary and 60 secondary.
Anybody have a better setup for a 400?

 

Are you using the 600 cfm or the 480? Start 47 or 48 on the primaries, and about 56 with the secondaries, and be prepared to change them. Each engine, rear end, vehicle weight, etc, is different.