BBD/motorcraft carb swap Q's

[sean]

I am grossly under educated with the world of carbs, however, I learned that a 2100/2150 motorcraft carb can replace my electronic BBD. I guessed when I grabbed one from an 80'econoline 351. I either can't find or don't know how to identify the carb I have. I know I need an adapter plate but need to be reminded of the source and part number. I did grab the carb with all attatched choke and vaccumey thingies but it may as well have come from the moon because I don't know what they are or what I need. Can someone shed some light please.

[Stuka]

there should be atad on the front held on by one of the top scews. This will have the info you need for getting a rebuild kit.Personally I would have grabbbed one from a pre 79, because they have less smog stuff on them. if the ford had a v8, you will need to rejet it most likely.

[sean]

I can't find a tag anywhere. Can I remove and or plug the vaccume features to make it any better.

[Cecil14]

You need to look on the driver's side of the carb. Behind the throttle linkage there should be a number, I'm guessing yours says 1.21 which is a bit big for a 258. You may be able to jet it down but a better one would have been from a 5.0 ford with a 1.08 on the side.

You can get the adapter from summit, can't remember the part number but it's a holley to rochester carb adapter.

Anthony

[sean]

O.K. now I did find the 1.21 on the side. So I'm guessing thats the size of the jets. If it's able to be rejeted will it be the only difference? Now if I should need to go in search of the 1.08 are there other primo qualities to look for? How and where do I find the proper jet for the 1.21?

[Cecil14]

The 1.21 is the venturi size, not the jetting. I don't know a whole lot about the jetting for these babies, but you may be able to nab the jets from a 1.08 and try then, they should fit.

Anthony

[sean]

I guess If I could find a 1.08 to nab the jets from then I could grab the whole thing. Would a rebuild kit include the jets? If so I wonder if I could just buy a kit for a 1.08 and install it into a 1.21.

[Cecil14]

Don't think my kit came with jets...can't remember. I think those are a bit too variable to come in a rebuild kit.

Anthony

[sean]

It looks like I'll need to start over and find the right carb. The 2100 with 1.08 venturi is the one I'm after. Until then I think I'll go with the nutter bypass and trick the metering pins into retracting so I can use the BBD for now.

[shambone]

I've been running the nutter by-pass for 2 years now, no problems. I thought about getting a 2100 ,but mine runs too good to tear it apart.

[sean]

Thanks for the input. I have an article about he proceedure done on a CJ7. Am I looking for the same wire coloring described for those rigs (purple/orange, I think)?

[Bryan]

Is the only difference between the 2100 and the 2150 the altitude compensator (or whatever its called)??? Also, is the 1.08 venturi size the smallest one available, and would that have to be jetted smaller to work with a stock 258? I have a 1974 258 with the 1 bbl, should I get a later year 2 bbl manifold and get an adapter or do they make one for a 1bbl to 2bbl.

[sean]

I'm not sure of all the differences between 2100 and 2150 but I think the altitude compensator is one. So far the 1.08 venturi is the smallest I have heard of. I did not hear it would need to be rejetted. I hope someone can grab the manifold question for you.

[Cecil14]

The compensator should be the only difference.

The 1.08 2100 should work fine on a stock 258, that's what I'm going to run so I'll report back soon as I get it up and running.

The 1.08 is the smallest I've seen also. It was on 304s, 305, etc. and the 258 is only 50 cubes bigger so it should be close enough to work with minor tuning.

Anthony

[Bryan]

thanks Cecil14 & Sean. looking forward to hearing reports. Is it worth looking for a 2150 instead of the 2100 cause of the altitude compensator?

[4x4n In A Cherokee In Colorado]

Good thread here...Learned somthin new today!

[Cecil14]

I think the altitude compensator was really just an emissions thing. I think if you tune the carb without it then you'd be ok. You may need to rejet a normal carb to use it in a higher altitude area(colorado, etc.) but that should be about it.

Now I could be totally wrong here, don't really know.

Anthony

[sean]

If anyone has firm info on the altitude compensation it might be the difference for me. I live at 4000ft and spend most of my time between say 3000ft and 6000ft. I know tuning for one or the other can be done but I'm all over the place.

[Cecil14]

If you move around a lot like that you may want to look for a carb with it, or get one separate, think it just bolts on. Not sure exactly what it does though.

Sorry I can't help more,
Anthony

[sean]

Don't worry Anthony you don't need to have all the answers. I'm sure someone can chime in. You have helped alot already. If you had planned the 2100 conversion, do you have a plan for the linkage? I also expect I'll need a new air cleaner assembly. As long as ya'll keep answering I'll keep asking. Thanks for everyones help.

[Cecil14]

There was a post here a while back that I printed out that pretty much gave the conversion step by step. If I remember the linkage was pretty close, you just needed to make a small piece to reverse the direction the cable pulled the butterflies. Looked pretty easy, I plan on that part like thursday or so.

Anthony

[Bryan]

Here is a page with some great info on the 2150 and how to rebuild, theory, & basics. It's a ford page but it definitly applies to us.
http://home.earthlink.net/~bubbaf250/2150carb/carb01.html

[sean]

Thanks for the link. It is great for those of us that have so little experience. Anthony, if you find the link w/ instructions you know who needs it. We'll all be waiting for an update on your progress after Thursday. Good luck.

[Cecil14]

Ok here ya go:

MC2100 swap (http://www.ifsja.org/ubb/ultimatebb.php?ubb=get_topic;f=2;t=018669#000006)

Good luck,
Anthony

[Bryan]

I have an older 1974 258 with the 1 bbl carb. Anybody know what 2 barrel manifold I should look for? I dont really want to pay for an aftermarket aluminum intake so I need to find an OEM junkyard manifold. Will a later year 2 bbl bolt right up or do I have to get the exhaust manifold as well? Ok, I'm gonna play stupid here for a minute....whats up with that funky exhaust/intake setup? are they easy to remove/replace and do you have to do both or can you do each one individually?

[Cecil14]

The '80 up 2bbl aluminum intakes are the best factory ones to use. You will need to steal the exhaust at the same time though, the mounting of both manifolds go together and are different by era.

Also got an update on the motorcrap linkage deal. I got everything on and hookup up last night and it wasn't too bad. The linkage on the mc hooks up towards the front of the carb and pulls down and hooks up towards the rear of the bbd and pulls down. Take a look at the two side by side and you'll see what I mean.

The earlier post I linked explains it pretty well.

Anthony

[Zorm]

Hey, if any one wants. I can find a dig camera and take pictures of my 2100 swap. The only peices I bought was the carb adapter and a little throttle extension for the eddlebrock 4bbl carbs.
I didn't remove anything off the ole carter carb or modify the 2100 to get my throttle cable to work, just modifyed the eddlebrock extension thing and its working fine.
Also if you find any type of 2100 carb and there is no little carb number tag, just remember the car.truck you removed it from. Most places can get you the rebuild kit you need with that info. Also the 2100 1.08 is the best one for the 258 conversion. I have one but think the jets are still to big. I got is from G4WAG here on the list and he had it rebuilt for off-road on his 360.
I was thinking about change the power valve in my carb to get better milage and when I talked to a carb guru up here, he told me that all I would need to do is change my jets (which never come in any repuild kit you get from these chain auto parts stores)
Ok too darn long already, but I love the 2100/92 H.O. 4.0 head combo. Now just to change my gearing.

[427CometGuy]

Sean, I did the 2150 swap onto my 258. I used a 1.08 carb from a 78 Ford 302 but the jetting was too large. I played around with jets for a week and wound up running 47's. At our altitude of 4300' they work great.
On a side note, I found out from the dealership that Ford no longer produces OEM jets for the Motocraft carbs, so finding jets might get tricky. I had ZERO luck around here until I happened upon a race shop where they had some left-over jets from project cars.
Good luck on your project!

Dave

[ January 10, 2004, 10:06 PM: Message edited by: 427CometGuy ]

[sean]

Thanks for the specific jet size. I went back to the pick n pull this weekend and traded my mistake (1.21/ 2150) for a 2100 w/ 1.08 venturi from a 71' ford. When I pull this apart for re-build, is there any way to identify the size of the jets at that time? A week of looking and guessing is to much down time for me.

[sean]

Oh, I just realized that your 2150 w/ altitude compensator might produce different results than the 2100 I'm going with. Anyone care to speculate.

[tgreese]

The jets are stamped with their size (hole diam in thousandths of an inch). Take the four top cover screws off, remove the air cleaner bolt, and remove the little clip to the choke linkage, and the top of the carb will come off. The jets are clearly visible at the bottom of the fuel bowl.

You can make a WAG (wild a** guess) at the proper jet size if you know the current jet size and the displacement of the new and old engines. Let's say your carb came from a 351 Ford - then the amount of fuel passing through the new jets should decrease to about 258/351 = .74 or 74%. Lets say the jet size now is 48, then the area of the fuel passage is pi r^2, or 3.14 * 24 * 24 = 1809. The new size is 0.74 * 1809 = 3.14 * x * x, where x is the new radius. A little algebra, and 48 * sqrt(.74) = 42. So here's the formula: sqrt(new_cid/old_cid) * old_jet_number = new_jet_number

[ January 11, 2004, 10:42 AM: Message edited by: tgreese ]

[sean]

I grab the simplest carb I can and you want to throw algebra at it. Good thing I helped put my wife through college ehh. My immediate challenge is that I didn't look at the displacement of the engine I got it from. I have to assume that with the smallest venturi available it could be a 289 or 302. Maybe someone can chime in with other options on that one. Suprisingly I do understand the math and appreciate the effort laying it down. In the absence of the original CID, where do I go? If you were to build an engine and have to build a carb to match where would you begin?

[tgreese]

It's a good guess that it was a 302... Just try it! smile.gif

It'll work ok if you get the jet size close - then look at the plug condition and jet up/down to get a nice brownish-tan on the plug. I think your kinda stuck with trial-and-error without something fancy like a dyno or an exhaust gas analyzer.

[sean]

Cool. Thanks again for sticking with me on all the questions. Checking the plug color makes great sense. Now it's just a matter of finding a source. As I admitted when I started I know very little about carbs but I feel much better about it now. I'm excited to rebuild my first carb, but even better is to give this old 258 a kick.

[mtn goat]

Originally posted by tgreese:
I think your kinda stuck with trial-and-error without something fancy like a dyno or an exhaust gas analyzer.What year is that jeep of yours, You may already have a exhaust gas analyzer (oxygen sensor) You can tune from that to get it exactly what you want.

[sean]

It's an 83", so yeah I do have an O2 sensor. I think I know where this is going but walk me through so I know the target and values I'm looking for. Lets put that sensor to good use one last time.

[tgreese]

I have bought Motorcraft jets from Parker Carburetion - look on his Holley jets page.

Some values Mr. Parker can't get anymore. You can change the size of jets with a drill and pin vise and solder. Too much work if you can get the size you want for a few bucks though.

[sean]

I stumbled on Parker Carburation last night and noticed the 47's suggested by 427CometGuy are discontinued. My closest option is 46 or 49. I'm sure I can work with whats available. I want to get it up and running before I manipulate the jets myself. I want to verify that the simple rebuild went proper before I add any factors. I'll try to pull the jets today to get the current size, then run the numbers to see what is really necessary.

[tgreese]

Oh, you don't need to remove them. You can see the numbers on the exposed face of the jets.

When you go to remove the jets that are in there, get a big screwdriver that fits the slot precisely in width and length and that is sharp. It helps to undercut the tip of the screwdriver a bit if you have access to a grinder and don't mind grinding on your screwdrivers. Clamp the carb to the bench, push down hard, and turn. All the jets in old carbs that I've removed have been really tight, and the brass jet is soft, so really bear down. If you have a screwdriver with a square shank, it helps to turn the screwdriver with a crescent wrench in one hand and push down hard on the top of the screwdriver with the other.

[sean]

Brilliant! Now I can tell how much you really know. I just taught myself that whole soft brass, clamp to the bench thing. I was just logging on to ask how tight those thing are supposed to be. Anyway, I stopped right where I was in case they don't need to come out. They are stamped 47F on the top. Chances are I'll be jetting down for more rounded performance. What do you think?

[tgreese]

Sean, I'd expect that the jets weren't that tight when they were installed, but 30 years of tight metal-to-metal contact has made the surfaces interlock. Holley sells a jet tool, but I don't know if it'll fit the Motorcraft jets - they look bigger than the Holleys. Mr. Parker would know.

A couple of points - if you want to change the jets later with the carb in the truck, then you need to break the current jets loose now.

My formula above says 43 or 44, but I expect that my formula underestimates the leaning-out of going to a smaller jet size. (If the reader is interested, I assumed plug flow above, whereas the flow through the jet is almost certainly laminar. I can elaborate, but it's kind of far-afield and academic.)

I would start out with a 44 or 45 if I had them, but the 47 will be ok as a start IME.

[sean]

Well tim thanks again to you and all the others that chimed in. Without all your help I'd be like a blind man in a dark room lookin for a black cat that isn't there. I did the math to determine the same 43.4 or something like that. I expect my elevation to come to play somewhat and future tuning or mods will allow variences. I know what I need to get and do with this project now its time to start ordering parts:
holly to rochester adapter
air filter assembly
carb rebuild kit
new jets
soon as it all gets here I'll get started. I'll try to report on the results.
Thanks again everybody

[Cecil14]

Hey guys, got my truck running tonight with the 2100 on it. Once I got the timing close enough she fired immediately, even at about 20 degrees temp. I've got some fine tuning to do tomorrow and may need to jet it down a bit but other than that it seemed to run real good. So far so good.

Anthony