Motorcraft 2100 Carburetor

Motorcraft 2100 Carburetor

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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.

 

22 thoughts on “Motorcraft 2100 Carburetor

  1. 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?
    MK

    • 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.

  2. 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?

  3. 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.

  4. 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.

  5. 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.

  6. 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
        Jan

  7. 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

  8. 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?

    thanks,
    harry

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