A tale of two carbureutors

[Helomedic1171]

So, while I'm finishing up a combination oil pan gasket, oil pump/pick-up, and battery cable replacement, I decided to go tromp through the junkyard. I hate the way the Carter BBD (I assume that's what I have) makes the AMC 258 i6 / 4.2l in our CJ7 idle and run. I couldn't believe my luck when I found what I'm fairly certain is a MC2100 or 2150 sitting, untouched, in a 1984 E-AMC 150 . I snatched it up, and since I have an older 2100 at the house I can use for parts, I giggled all the way to the local O'Reilly auto parts.

Here's the deal. I have a rebuild kit, I have both carbs, but which one is more desirable for use on my 85 CJ7 ? I plan to do the junkyard MPFI conversion sometime in the next year, but for now, I want it to run better til I get to that point. the carb on the left in the photos is the one I just found, the one on the right is a well-worn unit I got from a dude in Canada. they each have different features, but which one is the better idea for my CJ7 ?

I live in coastal Ga, so a choke is not necessary, and I can run a manual one if I need to or mess with the electric choke if need be.













here's the I.D. tag from the newer one I just found:



let me know what you think, I only know what the internet says about these things, and I've only scratched the surface, I think.

 

[Woolyworm]

They should have a number in a circle on the side - you want one that is 1.08 to start with.


Wooly

 

[IOPort51]

Go ahead and make the choke work as well, manual chokes are a PITA.

If you do a good job of this the thought of injection may fade to a more pressing issue. After changing to the 2100 MC I don't think FI is that big a deal. At least not if there is something for sure not what you want.

What you are doing, IMHO, is one of the the best mods you could make. It works quite well and is very cost effective. A lot of "bang for your buck" in this one.

 

[Helomedic1171]

Dang it, I forgot to add that, and now I can't edit the post. they are BOTH 1.08s. just not sure whether I should use the earlier or the later, bowl vent or no bowl vent, etc. or just rebuild the more complete, unbolt a few of the gizmos from it, and bolt it on my jeep and try it.

 

[IOPort51]

Which one is the kit for?

 

[Helomedic1171]

Go ahead and make the choke work as well, manual chokes are a PITA.

If you do a good job of this the thought of injection may fade to a more pressing issue. After changing to the 2100 MC I don't think FI is that big a deal. At least not if there is something for sure not what you want.

What you are doing, IMHO, is one of the the best mods you could make. It works quite well and is very cost effective. A lot of "bang for your buck" in this one.

Thanks. I really like the junkyard injection idea, and I'll still do it, but like you said, I have more pressing concerns. I just want it to not die at every red light and stop sign. if that means I run the MC2100 for a year or more, no worries. if it works, I'm fine with it. so many folks out there swear by them, and I almost bought a 1983 CJ7 that had the MC2100 and I think a duraspark ignition/distributor, but I may have imagined that last bit. I do know that with the MC2100 it really got up and went, and fairly quickly. The '85 we have is a slug. it barely gets out of it's own way and runs worse than anything I've seen in a long time. the fact that it runs at all is probably a testament to the Jeep legacy and the AMC258.

Our '85 curiously had the "team rush" upgrade on it when we bought it, so this just caps it off, along with a nutter bypass and some timing advance. This mod just makes sense, and since I now have the carb in hand, I just couldn't say no. And I'd be a liar if I said I wasn't giddy with the thought of gleefully removing 80% of the vacuum lines and silly emissions fittings infesting the poor thing's engine compartment.

As for the choke, I keep reading about reversing the polarity, but no one makes mention of how to physically do this. when someone says "reverse polarity" I think "ground the + and add 12V to the -". is that what I'm doing, or is there something else here? and I agree, I'm not a big fan of manual chokes either, but down here in the low country, I'll likely never need a choke except 6 weeks out of the year. So any input on which one I should use? I guess the better question is, should I run the one on the left as-is with a rebuild, or should I put the airhorn/choke tower from the one on the right on top of the carb on the left with the better butterflies?

 

[Helomedic1171]

Which one is the kit for?

the kit is for the one on the left, the "newer" one. if I use it, can I/should I remove any of those various cylinders or solenoids off of it when I use it on my Jeep?

 

[Woolyworm]

Ditto on the 2100 performance - they are awesome. I've got a manual choke on mine, I like being able to make it do just what I want when I want. The one on the left looks like it's in a lot cleaner condition.


Wooly

 

[Helomedic1171]

it sounds like it doesn't really matter which one I use as long as I use one that works. I disassembled both last night and started soaking them. I'll be using the one on the left unless someone gives me a really good reason not to. I'm removing the idle solenoid since I don't have emissions inspections where I live. I think the major differences I've found are the carb on the left in the photos has a bimetallic strip idle air valve on the air horn, a long shaft (2 stage?) accelerator pump, bowl vent, and also has two sets of metering rods in the booster cluster. the one on the right has a different type of valve for the idle air, and has a single stage power valve with no shaft, no bowl vent, and only one set of metering rods (I think that's what those are) in the booster cluster.

I have no idea if any of those things are better than the other, but since I have the kit for the "newer" carb and it all seems to work, I'm going to start there. I will say that's good that I decided to rebuild these, they had a good bit of dirt and gunk in there!

 

[Helomedic1171]

One other thing, the carb on the left had #50 jets, the one on the right had #47 jets. from what I read, I should use the #47s, correct?

 

[Fastatv]

One other thing, the carb on the left had #50 jets, the one on the right had #47 jets. from what I read, I should use the #47s, correct?

The jets are interchangable, best geuss the 47's might do you better with the Six. I would recommend building the newer/cleaner of the two. But beleive or or not, the kit might fit both carbs.

 

[Torxhead]

After you change jets, keep on eye on the spark plug deposit color. As shown in a repair manual.

 

[elwood blues]

I'm going to throw my hat in to the ring here to try to help you out.

Both are 2150's. The one one the right is the older of the 2. The one on the left is one of the last 2150 variants there were.

Here's the things I can tell about it (the newer one) just from looking at it. It's off an automatic Transmission vehicle (Transmission kickdown cylinoid), it's got a two stage power valve (that's why the power valve cover has the vacuum nozzle on it), it's got an electric choke, and it might (I'm honestly not 100%) be the version with the altitude compensator on it.

The older one; the thing on top, is part of the choke pull-off circuit. Without a choke, it's going to affect how the butterfly's open and close. Other than it's in pretty rough shape, it's missing the piece that goes in the breather hose, probably nothing that you don't already know.

IMHO, the older one almost looks deteriorated past the point of an at home reconditioning. The newer one, may be more complicated than you want. You can remove a lot of those things (automatic kick-down cylinoid, change the two stage power valve, etc) but that will end up affecting the carburetor and how it works.

 

[Helomedic1171]

The jets are interchangable, best geuss the 47's might do you better with the Six. I would recommend building the newer/cleaner of the two. But beleive or or not, the kit might fit both carbs.

Thanks! I think you're right, there are a lot of similar parts in the box, and I think some extra bits too. Also, when I saw the #50s, I was really hoping I'd find a different size in the other carb and I lucked out, now I have a couple pairs I can use to get it dialed in better.

After you change jets, keep on eye on the spark plug deposit color. As shown in a repair manual.

will do.

I'm going to throw my hat in to the ring here to try to help you out.

Both are 2150's. The one one the right is the older of the 2. The one on the left is one of the last 2150 variants there were.

Here's the things I can tell about it (the newer one) just from looking at it. It's off an automatic Transmission vehicle (Transmission kickdown cylinoid), it's got a two stage power valve (that's why the power valve cover has the vacuum nozzle on it), it's got an electric choke, and it might (I'm honestly not 100%) be the version with the altitude compensator on it.

The older one; the thing on top, is part of the choke pull-off circuit. Without a choke, it's going to affect how the butterfly's open and close. Other than it's in pretty rough shape, it's missing the piece that goes in the breather hose, probably nothing that you don't already know.

IMHO, the older one almost looks deteriorated past the point of an at home reconditioning. The newer one, may be more complicated than you want. You can remove a lot of those things (automatic kick-down cylinoid, change the two stage power valve, etc) but that will end up affecting the carburetor and how it works.

You're right, the newer one came from an 84 E150 with a small block and and auto. I was going to remove the solenoid, but what's wrong with the two-stage power valve? I have no experience with one vs. the other. neither carb has the compensator, but I'm fine with that. I have the older one soaking again in some chemicals, but the newer one cleaned up pretty well. if the older one doesn't have any play in the throttle linkage rod, it may be useful, but for now I'm just cleaning it up to see if it's salvageable.

what about the newer one makes it too complicated for this swap/mod? and how much effect are we talking if I change some things?

 

[elwood blues]

Fastatv makes a good point that the jets are interchangeable. 47/48 is good place to start, at a low elevation like us on the east coast. There aren't a lot of places that carry Motorcraft/Autolite carb jets, just know that they are NOT interchangeable with Holley carburetor jets.

You can remove the auto-kick down solenoid without any effects. The complications start when you start removing parts for the choke. The new carb has the choke pull-off solenoid there behind the electric choke. If you're going to turn it into a manual choke, you have to get rid off all of that stuff, and plug any of the associated vacuum ports. That's where you're going to start running in to issues is if you don't plug the correct vacuum ports.

The two stage power valve was a very late change in the Motorcraft/Autolite carb design. The two stage power valve is just what it says it is, instead of fully opening the power valve, there's a half-way open and full open. It was a fuel efficiency thing. The port has to be connected to a manifold vacuum source, and the 2 stage power valve are available in a bunch of combinations. Power valves ARE interchangeable with Holley carburetors. If you don't want to mess with a 2 stage power valve, you can swap the cover from the older carburetor and just run a single stage power valve.

 

[Helomedic1171]

Fastatv makes a good point that the jets are interchangeable. 47/48 is good place to start, at a low elevation like us on the east coast. There aren't a lot of places that carry Motorcraft/Autolite carb jets, just know that they are NOT interchangeable with Holley carburetor jets.

You can remove the auto-kick down solenoid without any effects. The complications start when you start removing parts for the choke. The new carb has the choke pull-off solenoid there behind the electric choke. If you're going to turn it into a manual choke, you have to get rid off all of that stuff, and plug any of the associated vacuum ports. That's where you're going to start running in to issues is if you don't plug the correct vacuum ports.

The two stage power valve was a very late change in the Motorcraft/Autolite carb design. The two stage power valve is just what it says it is, instead of fully opening the power valve, there's a half-way open and full open. It was a fuel efficiency thing. The port has to be connected to a manifold vacuum source, and the 2 stage power valve are available in a bunch of combinations. Power valves ARE interchangeable with Holley carburetors. If you don't want to mess with a 2 stage power valve, you can swap the cover from the older carburetor and just run a single stage power valve.

Cool! thanks! I'll start by running it with all the stuff still intact, and work from there. I was very careful about removing the electric choke assembly, but I can see lots of cracks in the plastic part of the housing, and the only thing keeping some of the big pieces together is the grease. I'm going to go hunt for a new one later today. If I can make this choke work, I'll keep it on there. I should have most of it back together today.

 

[elwood blues]

The electric choke covers, the black plastic piece you're talking about, are universal between carbs, every parts store should have one in stock.

 

[Helomedic1171]

I'm nearly finished with the carb, but I have a couple of questions. here are some photos:



and



Measurements shown are in 32nds of an inch. I've seen several measurements for float drop: 9/16" from the top of the carb at the rear of the float, the data table included with the rebuild kit instructions says 3/16" from the top of the carb from the front end of the float before the end radius (for a Ford AMC 258 i6 / 4.2l , I figured this was a good start).

Which measurement is correct? if neither are correct, what is the correct measurement and where do I measure it at on the float?

 

[Hedgehog]

I'd follow the instructions that came with the kit, the kit knows what the kit needs. Essentially the float will be level in the bowl when it shuts the gas flow off.

 

[mriplaybass]

Here is a very concise procedure for the 2100 / 2150 carbs. I used this PDF, and my carb works great. Might have even gotten this from somewhere on this site!