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post #1 of (permalink) Old 12-21-2002, 10:51 PM Thread Starter
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YJ - MC2100 Questions.

Like most everybody who has spent enough time living with a Carter BBD, I've decided it's time to chuck it in favor of something else.

I think I'm going to grab a MC2100, but I'm not sure if I should get a "rebuildable core", or go down to the local Autozone or something and get one there.

I found a carburetor shop that has the "core" MC2100's for something like $40, and a rebuild kit for that probably wouldn't run more than what, $15 I'm guessing?

1) Is the 2100 a direct bolt on to the stock 258 intake, or will it require an adapter (if so, where can I find an adapter)?

2) I know there is some modification that needs to be done to the throttle linkage and stuff to make it work with the stock setup, but how much is needed?

3) If I did go down to the parts store, is there a specific car and year I should get the 2100 for, like say a late 70's Ford Falcon or something?
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post #2 of (permalink) Old 12-22-2002, 01:12 AM
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Re: YJ - MC2100 Questions.

Alright.. being that this is the biggest swap I've ever done, and I got alot of help from here, I figure I'll chime in on this..
But make sure you remember next time someone asks for aid on this topic after you do the swap.

Rebuild? New? or what?

Well, I shelled out the cash for a new one. (rebuilt.) It's got a warrenty.. it's nicely done, and it's in good shape.. there's no pissing about it's ready to go on.
That was just me.. but atleast I knew that if it didn't work for whatever reason I could just take it back..

It ran me about $300 CDN... that's about $0.20 USD..

well.. not really.. more like $200..

there was a $50-$75 core fee.. The told the guy at Napa what I was doing.. and he must have realised that I've been in there alot, and will be back again if he could swing me a favor.. so he ignored the fact that the core I gave him back looked awfully similar to the BBD.

It's not a direct bolt on.. you need an adapter plate.. there's a good quote somewhere about adapters being so easy to make it should require a licence.

Bleh to them.. for $12.95 US who wants to piss around with that crap..
I bought one from Summit. The gauged me on the handling, the shipping, the brokerage. NEVER AGAIN.

I didn't know the local CDN tire carried those adapters..
IF you must, get it from them, if not, get it locally. (NAPA wll prolly order it for you)

Two choices on the throttle linkage. IT must pull back, not down. #1 is to adapt the linkage itself, That seemed sketch to me.. welding so close to the fuel system.. bolting kinda looked drab as well.. I opted to re-fab the bracket that my BBD had.. this is the bit that holds the outside of the throttle cable. it was a peice of steel bent in one place..
I pulled it out, made 2 or 3 cuts, smacked it with a hammer, drilled a hole and painted it. took all of 30 min and it was the first fabbing of my life. bolted into the original position, and makes the carb work like it should.. looks professional too.

As for the parts store..

Talk to the guys.. look at the book your self.. get the manager out and tell him what your doing.

Mine was an AMC 302.. CJ7 from between certain dates.. it's in the BOOK..

Just a matter of finding it.. make sure they are the #47 jets.. if the guy has a ounce of sense he will let you look at the book and figure out what you need. if not go elsewhere.

It's a worthwile swap.. and there's a great write up on here by someone.

easy as pie.. great to get you in the fabbing, bolting, wrenching move.

Took me.. someone who had only driven a Jeep and never worked on it.. about 2 and a half hours...

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post #3 of (permalink) Old 12-22-2002, 07:17 AM
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Re: YJ - MC2100 Questions.

Ferrite Rodent,

Id buy a used one and rebuild it, and buy the adpter!

they are dirt common and cheap in junkyards, on ebay, ask on here ( I sodl mine about 2 weeks ago on here)

a good kit is about $25, takes a couple of hours at most, and youll learn something that you might need again!

the only problem iv seen on them is that sometimes the bore thru the case where the throttle shaft goes thru will wear, and seep a little fuel out the sides of the carb, on the outside of the carb it will be obvious itll be oily looking below that shaft, try to avoid one in that condition.

there are fixes for it, but ive never seen one that didnt run because of that, they just sep gas.

they are the simplest carb automotive carb ive ever messed with.

stock application for a 1.08 venturi size is a late 70s CJ with a AMC 304 if you want to order one, it will run about $200 and buy you some peice of mind and less junkyard searching!

just another opinion!
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post #4 of (permalink) Old 12-22-2002, 08:15 AM
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Re: YJ - MC2100 Questions.

If you pull one off a Ford, make sure it has a pcv connection on the carb. Some don't have it on the carb, and you need it to keep your crankcase ventilated and the environment healthy.

Here's the info I've gathered on the swap. It's worthwhile, it does all the things a jeep carb should, idles well, makes power, runs perfectly on inclines.

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

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

This 2bbl 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. I am very happy with the conversion and thank all of those jeep enthusiasts who helped me with information on this swap.

This conversion will not meet with any legal requirements that prohibit the removal of original equipment or the tampering with emissions control equipment. Check with your local authorities if your vehicle will be subject to inspections in this regard.

The cost of this conversion will be approximately $150 or less using a junkyard carb you rebuilt yourself, rebuild kit, new air cleaner, adapter plate, and manual choke kit. You may opt for buying a rebuilt carburetor, and I would suggest that you order one made for an AMC 304.

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 accelerator pump linkage. As difficult as this is to measure in the junkyard, the 1.08 is the size of the venturis (the barrels). I have been advised that #108 is 450 cfm, #114 520 cfm, and #121 575. Use the 1.08. This carburetor body is cast from two pieces, a top cover and a combination baseplate / venturi / float bowl. 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 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 accelerator 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 and mine was labeled #16. I have been advised that this means that it will not enrich the mixture until manifold vacuum drops to 16 inches HG. I had to go to a carburetor rebuilder to get this part, it was $5.00. Take in your old one as a sample. A single stage may work fine as well.

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 like Holley’s. 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). I ended up fabricating an adapter to a K & N conical filter out of fibreglass.

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. Mark all hoses you remove from the Carter BBD and connect them back up to the corresponding ports on the MC 2100. The only connection missing from the MC 2100 I used, compared to the Carter BBD is the vapour line running from above the float bowl to the charcoal canister for the collection of evaporated gas fumes. I would suggest plugging this line that ran back to the canister, as the MC 2100 vents the float bowl into the air cleaner housing.

7. PCV – There is a large PCV inlet port on the rear of the carb at the base. If you are looking in the junkyard for a MC2100 be sure that the version you take home is not an older one missing this port.

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. The choke mechanism on my carb has a passage to the base of the carb where is picks up manifold vacuum. This draws heated air or exhaust from the larger fitting on the choke casting (which should also be capped off by you) and warms up the choke’s bi-metal coil. If you install a manual choke, you should plug the inner passage with epoxy or rtv sealant to reduce your idle speed and keep dirty air from entering the manifold.

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 Base plate – There is a cast aluminum base plate 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 base plate. I picked one up from the junkyard just in case. Using it will require lengthening the throttle linkage rod to compensate for its thickness.

12. Miscellaneous – The rebuilt carburetor 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. They are the same size as used on the 4 barrel motorcrafts. After a winter’s driving I have examined the spark plugs and am happy with the jetting which is #47’s. Both MC2100’s from 304 AMC’s I have seen came equipped with #47 jets. I have found that for my application the accelerator pump linkage works best set to the third hole down from the top (of four holes) on the arm at the throttle shaft. It’s easy to tinker with to verify of this works best for you.

Tim Martin
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post #5 of (permalink) Old 12-22-2002, 09:57 AM
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Re: YJ - MC2100 Questions.

My two cents is make your own adapter..

The only one I could find was made by transdapt--carried by everyone. This is the same company that makes your crome ignition coil covers. Their unit is really cheesy. It looked as if you accidentally leaned on the carb, the adaptor might just split in two.

I went the mo money route and bought a 1" spacer and a 1/2" Black and decker BULLET drill bit. the bullet bits are the ones with a small cutter in the center and a mostly flat cutting surface. WalMart carries them. The flat cut of the bit creates a nice little pocket for the allen head bolts to sit in. the rest is pretty self explanatory, but if you need help let me know. mine has offered no problems, despite the fact that my holes ended up off target because I used the trans dapt unit as a template!
post #6 of (permalink) Old 12-22-2002, 10:52 AM
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Re: YJ - MC2100 Questions.

I just welded the throttle arm off the carter onto the 2100. Here is a pic. I also made my own mounting adapter.

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post #7 of (permalink) Old 12-22-2002, 11:56 AM Thread Starter
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Re: YJ - MC2100 Questions.

Right on.

Thanks guys, looks like I have enough information to keep my head spinning for a few days. [img]images/graemlins/grin.gif[/img]
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post #8 of (permalink) Old 12-22-2002, 12:10 PM
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Re: YJ - MC2100 Questions.

) Is the 2100 a direct bolt on to the stock 258 intake, or will it require an adapter (if so, where can I find an adapter)?

As said, you need an adapter. I used a Mr. Gasket Motorcraft to Rochester 2B adapter. It was about $14 and took them one day to get it in stock for me.

2) I know there is some modification that needs to be done to the throttle linkage and stuff to make it work with the stock setup, but how much is needed?

I just took some flat stock and drilled three holes in it and made an "arm" and used some sheetmetal screws to mount it to the linkage on the carb. I had to drill one extra hole in the linkage and used a stud for the factory "pull rod". See pic.

3) If I did go down to the parts store, is there a specific car and year I should get the 2100 for, like say a late 70's Ford Falcon or something.

I wound up getting on for a 68 Bronco with a 289. It has a manual choke(which I wanted) and no PVC port. I drilled the adapter for the PVC and just used some scrap tube and hose to hook it up.

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