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Ford 4100 Carburetor Kits

CK14 FOrd 4 bl carburetor kit

CK14 kit for 1958-up Ford 4100 complete with secondary diaphragm

CK415 Ford 4 bbl carb kit
CK415 kit for 1957 Ford 4100 with early pump, complete with secondary diaphragm


Ford 4100 primary float
F25 Primary side float

F26 secondary ford 4100 float
F26 Secondary side float


Choke Thermostats

Ford choke thermostat
CC34 hot air choke thermostat

Ford electric choke thermostat
CC28 electric choke thermostat


Service Manuals


Ford 4100 Carburetors

The Ford model 4100 is an aluminum-bodied four barrel carburetor used from 1957 to 1969 on Edsel, Ford, Mercury and Ford truck products. Ford carburetors have also been referred to as Autolite and Motorcraft carburetors at various times.

The first design of the 4100, produced in 1957 only, used a different accelerator pump from 1958-up models and requires a different rebuild kit. Our CK415 services first design carburetors; all later models use CK14.

General Features

The 4100 consists of two main aluminum castings, the float bowl and the float bowl cover, or airhorn. Like the two barrel Ford 2100, the 4100 carburetor incorporates the throttle body as part of the float bowl casting. The venturi is cast into the float bowl and has removable booster venturi clusters as inserts. The size of the venturi in inches is cast into the left hand (driver's) side of the float bowl. The most common size is 1.08 inches and is found on smaller V-8s.

A brass or aluminum tag was attached to one of the front float bowl cover screws with the carburetor number. Identifying the carburetor if this is missing can be difficult. In some cases, part of the carburetor number is stamped on the left side of the base in front of the primary throttle.

Ford 4100 carburetor exploded diagram
Exploded diagram of a 1958-up automatic choke Ford 4100 carburetor



The 4100 uses two floats which are mirror images of each other and can only be used on either the primary or secondary side.


Most 4100s used an automatic choke. A few applications, such as 289 Hi-Po and some truck carburetors, had a manual choke.

The automatic choke is hot air operated. Cold air is warmed by passing through a tube which goes through an exhaust passage and then enters the rear of the choke housing. The warm air causes the bi-metal choke coil to expand, allowing the choke to open.

On some models there is a choke piston assembly which acts as a choke pull off: When the engine is first started, the choke is closed fully. When it starts, vacuum pulls down the choke piston which opens the choke slightly so that it can continue to run. The choke later opens fully as hot air warms the choke coil.

There are many variations on the 4100 choke system. Our CC34 choke coil can be used on most of these.

Where the hot air system is inoperative the existing hot air choke coil can be replaced with an electric choke thermostat. In these the choke coil is heated by an integral heating element in the choke cover - a hot air tube is not required. Full system voltage is supplied to the choke whenever the engine is running to keep the choke open. Our CC28 choke coil replaces the hot air choke without modification in many instances. In some 4100 carburetors the tang which engages the choke coil is too long and will interfere with the heating element inside the CC28 choke coil. In these cases the tang needs to be shortened to accommodate the electric choke. Alternatively, extra gaskets can be used between the choke housing and choke cover to supply extra clearance.

Secondary Diaphragm

The 4100 uses a vacuum operated secondary throttle. The secondary diaphragm pulls the secondary throttle open against a nylon stop pin on the fast idle adjusting lever. If the pin is missing or broken the secondary throttle can open under part throttle conditions. The pin must be in place and positively close the secondary throttle when the primary closes in order to prevent unwanted acceleration.

Two different secondary diaphragms were used on various models - a male one with a pin to engage the lever that connects to the secondary operating rod and a female, with a hole to engage the pin on the lever. Our kit CK14 contains the female diaphragm and a matching lever. The 1957-only kit, CK415, contains a male diaphragm since only that style was used in 1957.

A common source of trouble in the secondary system is warpage in the diaphragm cover. This can be overcome by machining the cover flat to prevent vacuum leaks.

Restoration Notes

In addition to air leakage around the secondary diaphragm cover, the power valve cover can also warp and can be fixed the same way.

The finish on most of the carburetor is natural aluminum. This can be restored using fine glass bead blasting, but only on a fully disassembled, clean and dry casting. The choke housing, secondary diaphragm cover, some power valve covers and accelerator pump covers are cast in zinc and are finished in a chromate conversion coating, discussed here.

Ford 4100 carburetor

Ford 4100 carburetor showing hot air operated automatic choke. On this model, a hot water hose is clamped to the choke housing to keep the choke warm after the engine is shut down, improving restarting of a hot engine.

Ford 4100 driver's side view

Driver's side view. Venturi size marking (1.12 in this case) is visible on the side of the float bowl. Part of the carburetor number is sometimes stamped in the area below the dashpot bracket in front of the throttle arm.