Autolite 4100 Carburetor

Autolite 4100 CFM Size
Venturi Size CFM
1.08 480
1.12 600
1.19 670

The venturi size is stamped on the side of the carburetor.

Find parts for your Autolite 4100.

Buy Your Autolite 4100 Carburetor Kit here.

A complete Autolite 4100 rebuild video is available on DVD.

Free Autolite 4100 Manual
Autolite 4100








Download Your Autolite 4100 Carburetor Manual Here

Autolite 4100 1968-69 Carburetor Manual – specific to the 1968-69 model.

Autolite 4100 Instruction Sheet w/Specifications

Watch a video about testing the 4100 check ball.

Need a New Check Ball Weight For Your 4100?
Autolite 4100Unfortunately these are not made anymore, but you should be able to make one without too much trouble. Here are the specifications: 
1. Brass
2. Length .89″
3. Diameter .125 1/8 welding rod should work.
4. Weight: 1 gram – 1 gram=035273 ozs.


Why does my carburetor lose the fuel after sitting

The fuel loss may be due to a bad fuel pump; they have
known to siphon gas out of the carburetor and back into the tank
through bad valves, or into the crankcase through a bad diaphragm.
Gasoline not has a lower boiling point and the ethanol
additive make it even worse. Some carburetors may be experiencing
percolation. After the engine gets hot and is then turned off, the
carburetor gasoline quickly boils out of the carburetor. I have no
magic bullet for treating the ethanol content of the gas other than to
visit  and hope that a gas station selling non-ethanol gas is located near
you. Obviously, anything which can be done to lower engine temperature
will reduce fuel percolation.
The problem may be warped venturi boosters. The fuel level sometimes stands above the base of those boosters, so you can see where it would be advantageous for the venturi and the bowl casting to seal together.

Carburetor Stumbles
Looking for suggestions on a 1963 390 w/4100 Autolite. Car started to
hesitate on start-up acceleration. Totally a new, overnight situation.
Mechanic noted timing slightly off and distributor was loose
(electronic ignition). Car ran better but secondaries had stopped
working. Installed new diaphragm. Solved secondary issue. Acceleration
issue persists, particularly when cold. Have replaced plugs and wires.

  • Made sure the main discharge check ball was installed
    and not leaking. There should be a pin (weight) on top of it. There is also
    an intake check ball (or red check diaphragm) in the pump. Both must be
    present for the pump to work.
  • An insufficient fuel level will cause the pump not to
    work. As I recall, the intake port for the pump is positioned fairly high in
    the primary chamber. Floats should be set to specs (not lower) or the
    pump my not have sufficient draw to operate.
  • Clogged pump nozzles will of course cause a stumble,
    and are more likely to occur with our modern gasohol helping to wash all of
    the accumulated dirt in the fuel system downstream to the carb.
  • If you adjust a Ford 2100 or 4100 by the spec sheet
    which accompanies most carb kits it will invariably have a stumble. You
    instead adjust it by eye and by feel so that the pump arm always keeps
    just a little bit of pressure on the push-rod in the middle of the
    accel. pump diaphragm, even with throttles closed. If you follow the
    instructions, you will always have a gap between the pump arm and the
    diaphragm push-rod . . . guaranteed. Great recipe for a stumble.

23 thoughts on “Autolite 4100 Carburetor

  1. Thanks for the 4100 manual. I’ve had a difficult time locating one until now. Your videos on Youtube are great as well. Thank you.

  2. Hi, we’ve got an Autolite 4100 that came off of a 64 Galaxie 352 FE Auto, the venturi size is not stamped on the carburetor anywhere. Is this a common sight to see with no venturi stamping on the carb? I assume it’s a 1.08

      • I found out that it’s a 1957 model, it says EDC where the 1.08 or 1.12 would be stamped.

        I want to convert it to electric choke, it has the piston-less style choke housing with the little flimsy type spring in the center, it also has that post that needs to be cut off. Will the choke thermostat cap that you sell for the Autolite/Motorcraft carburetors work on this style? I notice the third picture on the ad for the part number TH1023 is exactly the same as the choke housing mine is. The description of it was a little fuzzy to me, I’m not sure if you were describing the style I have (third picture of the ad) or a different style?


        • I too have just found a early carb and was told it is a 58.Has a date code of 11 57.I would like to find cfm also but there is no numbers stamped on base.It has also been taken from a Canadian Mercury.Is there any way to figure out size without stamping,I am hopeing for the smallest version for my Y block.

          • Look at the side of the carburetor. It should have the venturi size stamped. 1.08 or less was be preferred for a small block. 1.12 is marginal but will work. 1.22 is for big block. Sorry don’t remember the CFM.

  3. have a 1964 352 ford with 4100 carb, has misfire on cyl 1 4 6 7. which are fed on same plane on intake,can not find any vacuum leaks. noticed fuel is dripping from primary venturies at idle, float levels are fine, any ideas would be great, thank oyou

    • The venturies should not drip. I don’t know the carburetor history so here are some guesses.
      Main discharge should have a check ball and then a check weight. One or both could be missing.
      Check ball in main discharge not sealing. Hold the check ball down with a brass drift punch and pump the accelerator pump. There should be some pressure. If not tap on the ball gently a few times to seat it.
      Holes in venturi may be plugged. Use thin wire to clean out the holes.
      Venturi gasket not pressed down and may be holding up the venturi. The new gaskets don’t always fit perfectly and may need trimming.
      Fuel pump pressure too high. (bottom of the list)

      Thats all I can think of right now.

  4. I have a 65 tbird with a 4100 carb that the secondaries stick open on after full acceleration. The car is newly rebuilt with a kit I’m pretty sure I got from you. When the engine is off the secondary throttle plate lever is free and moves easily by hand. When the engine is running it is very stiff and hard to operate by hand. The vacuum diaphram will open it with no problem on full acceleration but it will not close. Any idea why?
    Thank you!

    • It seems obvious to me that something is rubbing, or binding. At idle you have full vacuum so operating by hand will have some resistance.
      Also do you have the spring behind the secondary diaphragm?

  5. “When the engine is off the secondary throttle plate lever is free and moves easily by hand. When the engine is running it is very stiff and hard to operate by hand.”

    The above is with the actuating rod removed

      • Yes. The engine runs fine and returns to slow idle when only the primaries are running. When stepping down on it it revs up fine but will not return to slow idle so in checking I found the secondaries were staying slightly open. I could rotate the secondary crank closed by hand but with substantial resistance so I removed the rod between the diaphragm and throttle crank and tried it by hand opening and closing it and there is a lot of resistance with the engine running. With the engine off it moves very freely. There is a spring in the secondary accelerator pump diaphragm. I have the carb off the engine now and the secondary pump apart and there is no check ball in there. I read somewhere that they run better without it so I’m wondering if I should put it back in. Do you think that is the problem or should I look elsewhere?
        Thanks Mike!

Leave a Reply

Your email address will not be published. Required fields are marked *