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Old 12-22-2000, 01:45 PM
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Default How to install Motorcraft 2100 in 258 jeep (detail

Motorcraft / (sometimes called Autolite ) 2100 Carb Install on 258 Jeep

Parts List: MC2100 Carburetor, adapter, air cleaner assembly, throttle arm replacement (fabricated).

This carburetor will replace the troublesome Carter BBD and produce a superior idle. It also appears to boost horsepower. It has a good reputation for being reliable and good off road. It is a larger CFM carburetor than the Carter and may produce some bog if slammed open at low RPM’s. I am very happy with the swap.


1. Motorcraft 2100 Carburetor – Sources: AMC 304 or Ford 302. Unfortunately Motorcraft does not stamp 2100 anywhere I can see on these carbs. The correct size will have “1.08” in a small circle cast on the drivers side of the carb body, somewhat obscured by the accellorator pump linkage. The throttle base plate has openings that are 1.550” on the 1.08 size model. This carburetor body is cast from two pieces, a top cover and a combination baseplate / venturi / floatbowl. Apparently you can set / observe the float height by idling the motor with the top cover removed. The top cover has the word “Motorcraft” cast into it on the passenger side above the float bowl.

Power Valve: Be sure to replace the power valve on this carb. It’s function is to enrich the mixture in two steps as manifold vacuum drops (signaling load increase). It is closed at idle, and opens to add more fuel as the manifold vacuum drops. If it is not operating correctly, your mixture may be too rich. It is located on the bottom side (front) and is contained under a cap with 4 screws. There is also an accellorator pump on the front, also under a cover with 4 screws, but it is identifiable by the accell pump linkage. I have obtained good results using an oem 2 stage power valve. This valve is longer than the single stage and is original equipment. It is 39mm long from top to bottom. I had to go to a carburetor rebuilder to get this part, it was $5.00. Take in your old one as a sample.

2. Carburetor Adapter – It is the 2 barrel Rochestor to 2 barrel Holley adapter. Also known as the large 2 bbl to small 2 bbl manifold adapter. Summit sells TD Performance Products adapter no. TRD-2086 for $12.75. It comes with 2 gaskets. I replaced the slotted bolts that came in the kit with allen head bolts to make tightening the adapter to the manifold easier. I also used a hardening gasket maker instead of the gasket between the adapter and the manifold (Permatex Form a Gasket 1A). I also used a Ford gasket between the carburetor and the adapter. It is made of black plastic and looks like two gaskets sandwiched together with plastic bushings inside the stud holes. Is this gasket necessary? There is nothing special about it other than that it will seal very well and also provide a lot of heat insulation from the manifold. The hole in the adapter is slightly larger than the jeep manifold. I have thoughts to switch to an aluminum intake manifold from an 84 and blend the manifold to the adapter with a die grinder.

3. Air Cleaner Assembly – This carburetor has a much large air cleaner base than the Carter BBD. It is the standard 5 1/8 “ air cleaner base used on most 4 barrel carburetors. Unfortunately the close proximity of the power brake booster and master cylinder limit you to a 9 to 10” (9” preferred) open element air cleaner. If you swap booster to a dual diaphragm GM booster (a great upgrade) you will not be able to use a filter above the carb at all. A K & N 9” filter (2” height) with top and baseplate is $49.39 from Summit (pn. KNN-601110).

4. Throttle arm – The OEM Carter uses a similar linkage, but pulls downward instead of the rear pull on the Motorcraft. You need to simply remove the throttle linkage ball stud from the Motorcraft, bolt on a small metal plate (1” by 3” and 1/8 thick) to the Motorcraft’s throttle arm with 1/8” bolts so it is rearward facing, and drill a new hole in that plate for the OEM throttle linkage. I would suggest bending a slight offset into the plate to move the ball stud slightly away from the carb to prevent binding of the linkage rod. In addition, bolt the plate on first then using the linkage rod, mark the plate for the new ball stud hole, remove the plate and drill the hole for the ball stud. Some people have removed the throttle arm from the old Carter BBD and bolted it on, but that seems like a waste of the old carb just to make a simple throttle arm with 3 holes in it. If you are not happy with this carburetor, you may need that old BBD back ( I doubt that will happen if you start with a healthy Motorcraft.)

5. Throttle return spring – I found that mounting the original downward pulling throttle return spring caused binding as it wrapped around the shaft. I instead fabricated a small bracket to bolt to a front bolt of the carb base to relocate the spring to the front.

6. Vacuum hoses – The motorcraft has two ported outlets. One on the front, just outside (to drivers side) of the drivers side venturi idle control screw. I used this ported outlet for my distributor. There is also a ported outlet on the passenger side of the carb base. I am not sure if there is any difference between these two.

7. PCV – There is a large PCV inlet port on the rear of the carb at the base.

8. Idle Adjustment – Like most other carburetors there are two screws on the front base to adjust the mixture. Turning them in leans out the idle mixture. Never seat these screws with a lot of pressure at they are needles which will distort and damage the soft metal of the carburetor. I would start with around 2 turns out on each screw and adjust equally from there using a vacuum gauge attached to manifold vacuum to adjust for peak lean vacuum. In other words, turn them out till you get maximum vacuum, then turn them in till it starts to drop off, and back them out slightly from that point to regain peak vacuum. This carburetor is very forgiving for idle adjustments, so don’t sweat it.

9. Choke – There was an electric choke assisted by exhaust gas on both of the MC2100 I looked at. I tried the Motorcraft electric choke and it did not seem to work well so I used the Carter BBD’s electric choke by removing and reversing the bi-metal coil inside. This worked well till temperatures hit –30 degrees and I switched to a manual choke. I found the electric came off too fast in these cold temperatures and annoyingly came back on after short stops. The manual choke works well.


10. Fuel line inlet – The original fuel line will work fine. You may want to replace the short metal section that screws into the float bowl with a brass fitting.


11. Ford Baseplate – There is a cast aluminum baseplate with a vacuum operated EGR assembly on it. These are common in the junkyards. As the oem gasket covers all of the bottom of the carburetor except the venturi openings I did not use the Ford baseplate. I picked one up from the junkyard just in case. Using it will require lengthening the throttle linkage rod to compensate for it’s thickness.

12. Miscellaneous – The rebuilt carb I used has a small spring on the float assembly shaft which I am told is used to dampen the float movement for rough conditions. The other MC2100 I have for parts does not have this spring on the pivot shaft. Jets are probably available from Ford. I am advised by a carb shop that they have had success with drilling and tapping the carb to accept standard Holley jets. I am waiting to take a further spark plug reading to see if any change in jetting is required. I have found that for my application the accellorator pump linkage works best set to the third hole down from the top (of four hole) on the arm at the throttle shaft. It’s easy to tinker with to verify this works best for you.

Tim Martin


84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, Lockright, full cage & belts, Xenon flares, AMC 20 1pc axles, GM dual diaphragm brake booster
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  #2  
Old 12-22-2000, 01:54 PM
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Default Re: How to install Motorcraft 2100 in 258 jeep (detail

This is great Tim. I have a good friend who is fighting with the BBD but isn't ready to commit to EFI yet. We have been considering the MC2100, but couldn't find enough info about the swap. The timing is perfect and I will definitely be monitoring this post to see what others have to add or ask. I hope you're ready for questions! People are going to love seeing this and I remember how many questions came up when Aaron posted the how-to for the TR upgrade. Thanks again.

'75 CJ5,258 w/Howell EFI,T18a,4.27's,33's,On-board air,Warn 8274
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Old 12-22-2000, 03:44 PM
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Default Re: How to install Motorcraft 2100 in 258 jeep (detail

When I rebuilt my 2100 a while back the kit came with a two stage power valve. There wasn't enough room in the cap at the bottom to put it in. The valve was to long. I beleive I have seen longer caps though. Did yours fit allright or did you have to modify for it? In what way does the two stage act different? I had to get a 75 power valve at a carb shop. The lower numbered ones at the parts store wouldn't even open. I beleive its because the 304 is out of a 71 J truck and it has no vaccum accesories at all and that keeps the vaccum higher. I can really tell when it opens but how does a two stage act?

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Old 12-22-2000, 04:15 PM
Carpal \'Tunnel
 
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Default Re: How to install Motorcraft 2100 in 258 jeep (detail

The cap over the 2 stage power valve is 22mm from gasket surface to top of cap (external). The two stage power valve will enrich the mixture in two steps, rather than just one. In other words you will get a richer mixture once the throttle opens to the point vaccuum drops to indicate part throttle opening, then it has another further step to open for near or full throttle (even less vacuum). Does the same thing as a single stage but in two steps for better mid range control of mixture enrichment. At wide open throttle, and idle, both will perform the same. This may improve fuel economy and driveability.

84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, Lockright, full cage & belts, Xenon flares, AMC 20 1pc axles, GM dual diaphragm brake booster
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Old 12-25-2000, 12:00 AM
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Default Re: How to install Motorcraft 2100 in 258 jeep (detail

I plan on putting a Motorcraft 2100 on my 88 YJ. I got the carb off of a 77 cj 5 with a 304. The carb had been rebuilt, but I am not sure what size jets i need to run. I am sure I am going to have to go down in size. Has any one else had any experience with this?

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