Motorcraft 2100 Carburetor

Motorcraft 2100 Carburetor

Check out our 2100 carburetor kits.




2100 Identification

Motorcraft 2100 Carburetor
Float Circuit
Motorcraft 2100 Carburetor

Motorcraft 2100 Carburetor Choke Circuit

This illustrates the flow of clean air and heated air which, together, act upon the automatic choke mechanism to properly position the choke plate. The channeling of comparatively cold and hot air into the choke housing adjusts choke plate position to accommodate ambient temperatures under which the engine is expected to operate. (Cold starts and engine warm-up periods are the usual situations which require a diminished air supply and resulting enrichment of the air-fuel ratio.)A single choke plate is located in the air horn above the two barrels. When this plate is closed, it provides the required high vacuum above as well as below the throttle plates. With a vacuum above the throttle plates, fuel will flow from the main fuel system as well as from the idle fuel system .. This provides the extremely rich fuel mixture necessary for cold engine operation.The carburetor choke shaft is linked to a thermostatic choke control mechanism mounted on the main body.The linkage between the choke lever and the throttle shaft is designed so that the choke plate will partially open when the accelerator pedal is fully depressed; thus, the unloader tang comes into operation and permits unloading of a flooded engine.Motorcraft 2100 Carburetor

The automatic choke is equipped with a bi-metal thermostatic spring and a vacuum piston. The bi-metal thermostatic spring mechanism winds up when cold and unwinds when warm. Thus, when the engine is cold, the thermostatic spring, through attaching linkage, holds the choke piston in its upward position and the choke plate in its closed position prior to engine start. Manifold vacuum channeled through a passage in the choke control housing draws the choke vacuum piston downward, exerting an opening force on the choke plate.

Then, when the engine is started, manifold vacuum, acting directly on the piston located in the choke housing, immediately moves the choke plate against the tension of the thermostatic spring to a partially-open position to prevent stalling.

As the engine continues to operate, manifold vacuum draws heated air from the exhaust manifold heat chamber. The amount of air entering the choke housing is controlled by restrictions in the air passages in the carburetor.

The warmed air enters the choke housing and heats the thermostatic spring, causing it to unwind. The tension of the thermostatic spring gradually decreases as the temperature of the air from the heat chamber rises, allowing the choke plate to open. The air is exhausted into the intake manifold.

Slots in the piston chamber wall allow sufficient air to bleed past the piston and into the intake manifold. This causes a continuous flow of warm air to pass through the thermostatic spring housing. The spring remains heated and the choke plate remains fully open until the engine is stopped and allowed to cool.

The choke rod actuates the fast idle cam during choking. Steps on the edge of the fast idle cam contact the fast idle adjusting screw. Thi s permits a faster engine idle speed for smoother running when the engine is cold. As the choke plate is moved through its range of travel from the closed to the open position, the choke rod rotates the fast idle earn. Each step on the fast idle cam permits a slower idle rprn as engine temperature rises and choking is reduced.

During the warm-up period, if the engine should reach the stall point due to a lean mixture, manifold vacuum will drop considerably. The tension of the thermostatic spring then overcomes the lowered vacuum acting on the choke piston and the choke plate is moved tow a r d the closed position, providing a richer mixture to help prevent stalling.

The linkage between the choke lever and the throttle shaft is designed so that the choke plate will partially open when the accelerator pedal is fully depressed, This allows the unloader tang to contact the throttle lever and permits unloading of a flooded engine. Motorcraft 2100 Carburetor

Adjusting Idle Mixture

Set your idle speed to manufactures specifications.

Turn your idle mixture screws in until they gently seat, then turn them out 1 to 1 1/2 turns.

There are several methods you can use to adjust the idle mixture screws. One way is to hook up a vacuum meter, then turn the mixture screws, one at a time, in 1/4 turn. Do this until the vacuum starts to drop, then back the screw out 1/4 turn. Alternate between each idle mixture screw.

Fast Idle Adjustments

Motorcraft 2100 Fast Idle

Motorcraft 2100 Fast Idle
Idle Circuit

Motorcraft 2100 Carburetor

Accelerator Pump Circuit

Motorcraft 2100 Carburetor

The accelerator pump circuit illustrated is a means of compensating for fluctuations in fuel demands during acceleration.

When the throttle is closed, the diaphragm return spring forces the diaphragm toward the cover, drawing fuel into the chamber through the inlet. The inlet has an “Elastometer” valve which uncovers the inlet hole to admit fuel from the fuel bowl. The valve covers the inlet hole when the accelerating pump is operated to prevent the fuel from returning to the bowl. A discharge weight and ball check prevents air from entering from the discharge nozzle when fuel is drawn into the diaphragm chamber.

When the throttle is opened, the diaphragm rod is forced inward, forcing fuel from the chamber into the discharge passage. Fuel under pressure forces the pump discharge weight and ball off their seat and fuel passes through the accelerating pump discharge valve and is sprayed into each main venturi through discharge ports.

An air bleed in the wall of the accelerating pump fuel chamber prevents vapor entrapment and pressure buildup in the diaphragm chamber.Motorcraft 2100 Carburetor

Main Circuit

Motorcraft 2100

Motorcraft 2100
Refer to the illustration and trace the interaction of air, fuel, and vacuum when the engine is operating at part throttle in its cruising speed range.

At a predetermined venturi vacuum, fuel flows from the fuel bowl, through the main jets, and into the bottom of the main well. The fuel moves up the main well tube past air bleed holes. Filtered air from the main air bleed enters the fuel flow in the main well tube through holes in the side of the tube. The main air bleed meters an increasing amount of air to the fuel as venturi vacuum increases, maintaining the required fuel-air ratio. The mixture of the fuel and air is lighter than raw fuel and responds faster to changes in venturi vacuumn. It also atomizes more readily than raw fuel. The fuel is discharged into the booster venturi where it is atomized and mixed with the air flowing through the carburetor.

The throttle plate controls the amount of the fuel-air mixture. admitted to the intake manifold, regulating the speed and power output of the engine.

A balance tube is located in each barrel directly below the booster venturi. When decelerating, the balance tube siphons off any excess fue1 droplets remaining around the edge of the booster venturi and discharges the droplets in to the equalizing slots in the base of the carburetor where they are mixed with the idle fuel.

The balance tube also acts as an additional air bleed during the idle fuel system operation.
Power Enrichment Circuit

Motorcraft 2100 Carburetor

Motorcraft 2100 Carburetor
The picture illustrates the power enrichment circuit in a typical Autolite-Ford 2-V carburetor. The activity which takes place in this circuit to handle performance under heavy load or high speed conditions is controlled by in� take manifold vacuum.

Manifold vacuum is transmitted from an opening in the base of the main body, through a passage in the main body and power valve chamber to the power valve dia�phragm. The manifold vacuum, acting on the power valve at idle speed or normal road load conditions. is great enough to hold the power valve diaphragm down, over� coming the tension of the spring on the valve stem and holding the valve closed. When high power operation places a greater load on the engine and manifold vacuum drops below a predetermined value, the spring opens the power valve, Fuel from the fuel bowl flows through the power valve and into passages leading to the main fuel well. Here the fuel is added to the fuel from the main fuel system, enriching the mixture.

As engine power demands are reduced, manifold vacuum increases. The increased vacuum overcomes the tension of the valve stem spring and closes the power valve.

Electric Choke Thermostat
Note: The 2100 carburetor didn’t come with an electric choke. The information below refers to a 2100 that has an electric choke thermostat retrofitted.

Since there is only one terminal on the choke housing do I need to separately ground the carburetor?
You should not have to do any grounding. The metal ring that fits around the thermostat is of course grounded to the choke housing by the screws and you will notice it also contacts the metal striping around the thermostat. You do however, need to make sure the mounting ring isn’t corroded, or rusted.

When the engine is cold I turned the choke housing until the choke flap on the carburetor was closed.  Is that the correct way to set up the choke?
Basically that would be correct assuming it isn’t closed too tight, nor should it close all of the way. There are a couple of adjustments that need to be looked at concerning the choke which is illustrated very well in the carburetor kit instructions. I will make a point to post the instructions here as soon as I get the time.

–          When the engine has warmed up the choke flap does not open unless I rotate the choke housing
There could be a problem here. Insure that you are getting 12v only when the key is on to the choke + terminal. Using an OHM meter put one lead on the + terminal and the other on the metal striping that is on the outside of the plastic choke cover. You should get a full circuit here. If not, then the thermostat is defective and should be replaced. You can do the same test to make sure you have a good ground by moving the lead from the metal striping to the choke housing.

–         –          Do you sell the components for the OEM heat riser/vacuum setup for that carburetor?  (going in a 1978 Jeep with AMC 304 V8)

At this time we only sell what is part of the carburetor.

Free Motorcraft 2100 Manuals
Motorcraft 2100 4100 Carburetor Manual

1968-69 2100

Watch a video about rebuilding the 2100.


69 thoughts on “Motorcraft 2100 Carburetor

  1. Mike, the 2100 is a great carburetor but have noticed if it sits for more than a day or two it takes a lot of cranking to start. The fuel bowl itself, has plenty of fuel. It isn’t evaporating. If I first pour about a tablespoon of fuel down the carb throat, it starts right up. Many people have noticed this “feature”; what is the cause? Even better, what is the fix? Thanks Mike

    • Gas these days has a low boiling point and evaporates much quicker than it used to.
      Check any vent line and gas cap going to the fuel tank. If plugged a vacuum will be created that sucks the gas out.
      Make sure the vent on the top of the float bowl is not blocked.
      Pull the carburetor off, sit it on paper, fill the bowl with fluid. Look for leaks out the bottom overnight.
      May be percolating. Engine gets hot, turned off, the fuel boils and evaporates out. Try other brands of gas. Look for ways to cool the gas. Rerouting gas lines, etc.
      Needle may not be seating. If new wipe the viton tip with mineral spirits.
      Test the fuel pump for the correct pressure. Around 4.5 lbs would be good, but refer to your motors manual.
      Installing an electric fuel pump with a regulator would be the last thing to try.

        • I believe he is referring to “hard starting” after sitting for several days. I found a simple answer – I wasn’t giving enough pumps before starting. In below zero temps, I found about 20 to 25 pumps was about right. Sounds like a lot, but it starts right up. 5 or 6 in more normal weather.

          • I would be careful with so many pumps. That would flood most cars, but since I don’t live in below 0 weather, I can’t say for sure.

  2. I have a 1969 Mercury Marauder with 72,000 original miles. I have a Motorcraft 2100 carburetor, the tag has D4PE EC stamped on it. I am trying to find the correct rebuild kit, can you help me?

  3. Hi Mike, My ’66 289 is fitted with a replacement Motorcraft 2100 carb code 6P that I have found on the internet as ‘being replaced under warranty from Ford standard stock’.

    To minimise inventory during warranty apparently they used a 1.01 venturi carb on multiple vehicles. The cfm for a 1.01 is 240cfm and the normal 1.08 is 287cfm. Surely the 47cfm reduction is going to significantly impact performance?


    Steve (UK)

  4. Mike, thanks for the response. I was unable to really chase this thing down so I went back to basics. From the instruction sheet that came with the parts kit I bought from you, I originally by passed the 2nd or 3rd step that shows how to adjust the choke pull-down to spec. My carb butterfly plate had a gap of 3/16″ at the low edge of the butterfly. The instructions for my car 73 cougar 351c, says “NONE”, but some say “- – – -“. Can you explain the difference, because as “NONE” I assumed the distance should be ZERO clearance.

    The problem was twofold. The adjustment screw on the bottom side of the airhorn was froze- freed up with a mix of ATF and Acetone. Got it moving so that the front of the butterfly has no gap to the airhorn wall, but this does not feel right to me. Does NONE perhaps mean that I should not have moved this screw?

    Can you do a video, or at least a thorough explanation please.

    • It may be that when you start, then choke opens slightly. If that is the case then it is OK, otherwise I would give it 1/8″ clearance. Also if there is a hole in the choke valve (butterfly), then it can be closed. The hole will allow some air in on initial startup.

      Sorry i’m not going to be able to do a tutorial on this at this time.

  5. Hi Mike, Great vids and instructionals you put out- Thanks. Question: I just rebuilt a 2100 for 351C (73 Cougar). I have the mixture close. I have the solenoid and curb idle speed dialed in. The choke is electric with 12v at start and ON only. The choke was set as per your vid- just closed and am 1/8th + or – more. I set the choke/throttle linkage for a cold start and it fires right up- the idle runs up to 1500 RPM and an minute or so later depending on the outside temp, I tap the accelerator and the carb runs down to 625 rpm as per the emission decal. SOMETIMES though a few seconds after Start-up the rpms will drop and the engine simply dies. (Without touching the accelerator pedal). What might cause this?

    • Do you step on the pedal slightly to allow the fast idle cam to move. Might be at hot position and being held there by the linkage.

      Next time it does that take a look at the fast idle cam. Is it on fast, or slow idle. Could be sticking.

  6. 1973 ford 302 pickup won’t idle. idle screws out 11/2 turns. runs good at everything but idle. only way will run is continuously patting accelerator at idle. any ideas where to start?

  7. HI,

    Does your 2100 kit come with a power valve? I ordered a rebuild kit with float recently. Carb has 1.21 venturi but not sure I ordered the right kit..

    My 2100 did not have a clip from the needle to the float. Is it possible for it to run like this? Car ran well for a long while. Carb was a rebuild from National Carb.
    I did use carb cleaner to flush the idle circuit once, but those clips are in there pretty good so I can’t believe I dislodged it.

  8. Hello Mike

    Have a professionally remanufactured 1.02″ venturi 2100 w/manual choke installed on a 292 Ford Y block, this is the OEM carb basically. Runs great, but noticed after a few days – maybe a week – the carb bowl must be empty because it takes a long while to start. Is the fuel evaporating I wonder, or internally leaking?

    The carb out of the box is considerably leaner than the Holley 2300 500 CFM 2bl it replaced. Never needed the choke till now.

    Cruising at 70 mph noticed pulling the choke out fully has no effect. Too lean? Plugs look OK, but it’s hard to tell with today’s fuel. Thanks for your time.

  9. Mike,

    I have a 1966 F100 with a Autolite 2100 manual choke. I have fuel leeking out around the choke side near bottom. I had the carb rebuilt by a business in Sacramento area and have spent a significant amount of money so far. Can you help?

  10. Just bought a fast idle lever for a 85 ranger 2150 2bbl from you guys I installed and now my “flutter” doesn’t open automatically, if I keep it open all the way what damages can occur?

    • Keeping the valve open all of the time will make it difficult to start in cold weather and most engine wear is when the engine is cold so you want it to warm up as fast as possible. The choke valve helps in this regard.

        • Update on my Autolite 2100 carb issues. After experiencing flooding and other issues. I rebuilt the carb again and found; the power valve gasket was torn. Apparently I over tightened it or the car backfired and blew it out. I also found that the little nitril check valve stem in the bowl was sticking out too far and binding the float up. After the Second rebuild, the car runs much better but…. Could still use some fine tuning. However, This engine still has no get up and go. Maybe it’s time for a rebuild or upgrade.

  11. Hi Mike. I recently rebuilt my Autolite 2100 carb in my 1970 Ford Torino w/ 302-2V. It was running fine using a gas can in the grill. After replacing the tank to fuel pump lines with stainless lines, new fuel pump, Now it stalls under a load…. But will idle fine for a couple of minutes then dies. I’m smelling gas in the oil now. Would this be poor adjustment or power valve issues or a flow issue? Adjusted lower screws in until stopped then out approx 1.5 turns. The float and needle valve are approximately 7/16″ from the top of the bowl lip. I have linked a YouTube video with a video of the carb top removed. It’s been 20 years since I have worked on carbs. Help! 😀

    • The video is a great help, but I couldn’t see what the float was doing. Was it close to level when it started out? Looks like the float is low, but again, I can’t see it. From what I can see, it appeared that the fuel ran out of the bowl. Is that correct?

      The fact that it ran Ok out of a gas can makes me think it’s a pressure problem. Test the fuel pump for pressure and compare with the spec from your motors manual. I would guess anything over 5 would be too much. New fuel pumps are especially suspect. I’ve seen then over 20 lbs, which isn’t your problem, but could be too low.

      Here is an article about testing the fuel pump:

      Also maybe the needle is sticking closed. Do you have the clip from the float to the needle installed? Can you move the float while running to see if fuel starts flowing again.

  12. Hello Mike. My question is about the bi metal spring and general choke on a 2100 fitted to a 66 Mustang.
    A/ it correct that the spring winds up tighter and smaller when you rotate the black cover housing counter clockwise (Richer)?

    B/ Do these springs usually give trouble or loose their ability to function correctly with age?

    C/ Can you supply a manual of how to set up the adjustments on the fast idle / choke plate relationship?
    Thank you. Alan in Western Australia

  13. Mike i have rebuilt my yfa. On my 258 cyl. And it will just start leaking gas out the bottom around base. Of the bowl please help ty..

  14. I am running a 2100/2150 on a vw type 4 motor (412/porche) I rebuilt the carb because I wasn’t getting any gas. The problem I am having is if I pump it and then start it it will run as long as I am pumping gas to it it will not start and idle I tried setting the screws at 1 1/2 to 2 as suggested still can not get it to idle any thoughts?

  15. Hi Mike

    I run pump gas 92oct.
    has ethanol in it. any more than 2 then?

    it’s tough to test because it’s a stockcar.
    can’t shut down to pull a plug. must cool down (1 lap) + taxi to the pits.

    She does get super hott!


  16. Hello Mike

    I run a 1.23(1963) on a 351w in my factory stock racecar.
    It runs lean at top end.(6200rpm)

    Do you have any Q&A’s I can read?

    I use no choke, butterfly was removed.
    uped the jets.
    Will a 1.33(1964) be a better choice?


  17. Hey Mike,

    I have a ’65 Mustang with a 289. The previous owner left a C4DF-S Autolite 2100 carb on this 289, venturi 1.02. My question is, do you know what the proper dry and wet float settings are for this carburetor? The rebuild kit only had the dry side at 1/2″ but no wet setting. I look on the web and you get all types of answers since there are so many different 2100s out there. I don’t know what I can trust. I’d like to hear from your experience, what you believe the proper float settings are. Thanks.

  18. Thanks Mike.
    The 66 Mustangs with the Autolite 2100A have a reputation for running
    “Filthly Rich” would you suggest reducing the main jet sizing down from 49F and or the power valve designation when rebuilding the carburettor?


    • I would only change the jets if the spark plugs are black. If the plugs are gray, then the jets are fine. .047, or .048 is good for most Mustangs, so it could be a bit rich, but again look at the plugs. Being wrong will damage the engine.

  19. What is the best liquid cleaner to soak carburettors in to bring the alloy back to “as new” appearance? I have tried carb cleaners, degreasers however these just don’t do the job and remove oxide back to new appearance. Thank you. Alan

  20. Mike
    Just replaced jets on an MC 2150 and the float will push down with pressure but I cannot get it to go up… did I get it back on wrong?

  21. I have a 2100 motocraft on a 74 F-250 360 FE. Its runs horrid really rich and dumps all fuel out of gas tank like 1 gal of gas into oil pan in 10 mins of running I rebuilt carb and put new fuel pump on and still have gas in my oil. So now Im looking for the problems. When I have carb on the bench with top off , I poured gas into bowl the float works but bowl will empty out the bottom out of a small hole in like 20 seconds I guess above the power valve. Is this normal??

  22. Hi,
    I have ordered the electric choke for my 2100. My carb no longer has the tube frm the manifild to the choke housing nor does it have the piston and bimetal spring (I just bought the truck) The electric choke has its own spring, does it need the tube from the manifold? What about the tube where the piston used to be, do I plug it?


  23. Mike,
    I need to order a rebuild kit for a 2100 for a CJ5. I have 2 carbs, one that came off of a parts jeep with a 304 V8 and the other I picked up locally. The parts jeep has the 1.08 venturi and 4OCA for the number on the base.(tags are gone on both of them). The other has minor differences but with 1.21 venturi and model number on base of 3ARB. I can’t find either of those numbers listed anywhere to cross reference them and get the correct kits for rebuilding. Thanks, Dale

  24. Dear Mike; Am at wits end here ,I have a 79 jeep cj5 w/ motorcraft 2100. However I don’ believe it is the correct year, I mistakenly bought a rebuild kit w/o taking in carb tag #. some parts fit others didn’t, I used what I could and cleaned and reassembled.
    setting to spec in my jeep factory manual. seemed to run great until I got out on the trail and it would on uphills and sucked down massive amounts of fuel (three quarters of a tank on a trail of maybe 15 miles. Its always died once in awhile on a steep hill but I could actually get 16 mpg on road. I screwed up somewhere!!
    Carb tag says D4PE EA 3M 17 Any help would be sincerely appreciated,
    Thanks Jan

      • Thanks, Mike. Since it is apparently not a carb number that was used on a jeep but from searching your website it shows up as off of a 73-74 ford 302 how can I get specs such as float level etc. or should I try to find and buy the right carb as shown in my Jeep manual ? Previous owner or owners must have switched carb, (they also mickey moused wiring smog control etc. but that’s another story) Thank you for your time

  25. Recieved a new plastic fast idle lever for my 2150 but can not get the old one off because it is trapped between part that hooks to choke pulloff. Can this part be removed or do i have to cut it at the top and seperate it and then jb weld it back together.

  26. My 68 Cougar has similar issues with the 2100 carb and a 302. I have to adjust all of the cam’s, and set screws I think after installing a rebuilt carb. Also, is the line from the exhaust manifold important for the choke or is it just for the air temp? Thanks.

  27. I have a Motorcraft 2100 2V on a 65 Mustang. The car is entirely original with 114K miles on the 289 engine that has not been rebuilt because it is running fine. I have rebuilt the carb, but I may have reassembled it incorrectly. If I adjust the idle mixture screws by turning them all the way in and backing off 1.5 turns, it appears to run rich and will backfire through the muffler during idle and deceleration. With the idle mixture screws out 1.5 turns, it idles OK. If I turn the idle mixture screws all the way in so they hit the stop, it idles better than if backed out 1.5 turns. Also adjusted all the way in, it very rarely if ever backfires. I have blown air through every passage and they all appear to be open. At both idle screw adjustments ( all the way in and 1.5 turns out) the cars runs fine. In summary, with the screws all the way in, the car runs fine. If I back them out 1.5 turns, it still runs fine but backfires through the muffler. All other systems on the carb (warm up, acceleration, etc.) appear to be functioning correctly. I set the timing to factory specs with a timing light with the vacuum advance disconnected from the distributor. Any suggestions on what is wrong?

    • You obviously have a problem and it isn’t the idle mixture screw adjustment. The adjustment you described are simply helping, or hindering another problem. If your float is Nitrophyl, did you replace it? You will need to take the carburetor apart again and make sure everything is as it should be. Float level, etc.

  28. My MotorCraft 2100, venturi 1.08 is continuing to run rich and with a large hesitation in mid-throttle. I’m currently running 20 inches of vacuum at idle. I have replaced the main jets from 47 to 46 and currently using 45. This is a 1979 Jeep CJ5, 258ci six cylinder. Most all engine componets have been upgraded, including ignition system and reworked head. I want to replace the accellerator pump and power valve. Will this solve problem? And what size power valve?

  29. just rebuilt my morotrcraft 2100 carb from my 65 mustang, currently will not pump any fuel into the the booster venturi/ main body of carb at start or idle. Carb runs no problem if I pour gas directly to start & keep throttle slightly as car cranks & runs.

    Trying to determine which part I need, float & needle seat working properly. I did replace the weight & ball. At start & idle no fuel is moving from the fuel bowl?
    Please advise?

    • Fuel to the booster, or primary discharge comes from two sources, via the main jets and the accelerator pump.

      So this off of the car.

      The best way to check out what is going on is to remove the top of the carburetor and add some gas to the float bowl. You need to start from the basics and work your way forward. Remove the venturi, then pump the throttle so that the accelerator pump is exercised. Fuel should come out of the main discharge. If not, then there is something clogging the accelerator circuit, or the pump is installed incorrectly.

      To check the main jets, blow air through the jets and see if air is making it all the way through to the discharge. If not, then you have a restriction somewhere.

      If fuel is getting to the main discharge, then your problem is probably with the venturi. Some of the holes are very small and can clog easily. Try to clean the holes without enlarging them any.

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