MC 2100 gurus please

1979bettywhite · Post by **1979bettywhite** » Thu Dec 21, 2017 3:21 pm

So when I got the chief, the fast idle cam was flipped up so that it would not engage in startup when the engine was cold. No big deal, start the engine, give it some throttle, hold it there for a bit until it will hold an idle and warm up.

I always had the intention of once again getting the automatic choke to work. Did this on my CJ when I first got it and it works flawlessly now.

But the MC2100 has me totally stumped.

The main issue: I can't get it to kick down/disengage as the engine warms. It basically wants to sit between the first and second step on the cam. Causing the idle to stay around 800-1000.

So here is what I have done:

Followed the TSM process to a T. Took the bone cold engine, set the fast idle cam on the second step, disconnected the heat tube, back off the fast idle cam screw three turns, started the engine. Choke pull down works fine and gap to air horn wall is perfect (9/64). Next I reset the fast idle cam screw three turns in, and then set the gap to the air horn wall for the fast idle cam screw (7/64).

Got her up to temp, hooked up a tach and set the fast idle to 1500 or so when on the second step.

Bliped the throttle and she won't come all the way off to curb idle. Just sits where I mentioned before.

Drove around for 30 min and she still sits about halfway between the first and second step on the cam.

I know the cover and spring are fine as well as the hot air tube, piston etc. Can feel hot air coming in with the cover off.

It's almost like the butterfly can't fully open.

So I am almost at my with end unless I am missing something.

Should the tang that the choke cover spring pushes against be giving some resistance, or what causes that to continually try to open the butterfly. That seems to be my problem.

I have read and researched a lot but I can't seem to find anything on this particular issue.

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letank · Post by **letank** » Fri Dec 22, 2017 11:21 am

1979bettywhite wrote: Bliped the throttle and she won't come all the way off to curb idle. Just sits where I mentioned before.

May be the throttle stop solenoid is sticky, check for the solenoid return to whatever is proper -or disconnect lead for testing-

Make sure that it is not binding on the driver's side throttle screw at the base of the carb

If you have all the smog system installed, sometimes, somehow the PCV feed to the charcoal canister developp a leak , the diaphragm on the charcoal canister has hole(s) and will hold up you throttle linkage up. Test the charcoal diaphragm w vacuum pump or disconnect and plug -I forgot how I tested it, it was too long ago-

tgreese · Post by **tgreese** » Fri Dec 22, 2017 12:06 pm

Maybe you can show a picture of the carburetor in situ?

You realize that the choke is thermoelectric, and it needs both the hot air from the choke stove in the manifold, as well as the electric resistive heating to open.

You are sure that the slot in the tang on the choke butterfly goes over the end of the bimetal spring.

If you twist the choke cover so the spring is fully loading the flap toward open, will the cam come off fast idle then?

1979bettywhite · Post by **1979bettywhite** » Wed Dec 27, 2017 4:15 pm

Alright, here are some pics of the setup. Sorry for the delay. Christmas happens.

I moved my heater hose from the location you see in these pictures to right up next to the choke. Zip tied it just to test things out.

Placed the cover spring in the slot of the butterfly tang and turned to close the choke just barely. Almost no finger pressure to open the plate.

Started her up and warmed it up. Gets all the way warm but still won't kick down. Idles on the second step of the cam at around 1000 rpm. Never really comes down from that and the plate never fully opens unless I press down on the fast idle cam linkage to force it off fast idle. But if I hit the throttle at all, it jumps back up onto the cam between the first and second step, thus idling again at 1000 or so.

Any thoughts? To answer the questions posed, it is a standard automatic choke. Works solely off of manifold heat from the tube. No electricity involved. Also, I don't think I have a throttle stop solenoid, or at least not the kind I'm used to. Should I have one? (Still learning). My carter 2bbl on my CJ does have one.

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tgreese · Post by **tgreese** » Fri Dec 29, 2017 9:05 am

The CJ is different! Do not make assumptions about a Motorcraft based on a Carter, or vice-versa.

The '79 wiring diagram shows a connection for the thermoelectric choke via an oil pressure switch (and an anti-diesel solenoid). A quick reading of the TSM text does not mention an electrical connection, but I believe the wiring diagram. I have never seen a choke cover on a 21xx activated exclusively by hot air - they are all thermoelectric, and have a push-on connection on the choke cover. The BBD (your CJ Carter carb) is entirely hot air activated. The two covers are not interchangeable - the sense of rotation is reversed, ie installing a BBD cover will close the choke as it heats up, not open it. You can take the spring out of a BBD cover, flip it over, and have the right sense of rotation. I have tried this setup on a 2100 and been underwhelmed with how it works.

Again, set the fast idle on and turn the choke cover so that the choke flap is wide open, and see if the fast idle cam will unload. If it will not, there is a problem in the linkage. If it does unload properly, you have the wrong choke cover, or it's not activated properly.

letank · Post by **letank** » Fri Dec 29, 2017 9:37 pm

This is a non thermoelectric choke like on the 74..
So we have a real 2100.
A bit late... but disconnect the cruise control... at the throttle to check for any binding.

1979bettywhite · Post by **1979bettywhite** » Fri Dec 29, 2017 9:48 pm

Yes, I believe it is a real 2100. I do see what you are saying though on the wiring diagram. It shows a red leaf going to the choke. Although all the pictures of the 2100 in the carburation section show nothing on the cover. I guess I could look for that connection since mine is not hooked up and I have converted over to a mechanical oil pressure gauge.

And yes, the BBD is the reverse. Did not even attempt to try and swap that cover over. I converted it to an electric choke a year or so ago. Has worked nicely on there.

I could just convert this one over to an electric choke solely, but I think the hot air helps to really make this work properly even if in conjunction with a 12v electric source.

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letank · Post by **letank** » Sat Dec 30, 2017 8:20 am

Btw you are missing one of the hot air tubes under the carb / thermostatic choke.
With the lack of solenoid recheck the complete closing of the throttle. On the driver's side there is the adjuster screw close to the base of the carb

letank · Post by **letank** » Sat Dec 30, 2017 3:46 pm

otherwise I have a pict of my fast idle cam on the 2nd step

if the pict diseappears, check on my links and go back from fuel and brake lines to the FSJ subfolder

Driftwood · Post by **Driftwood** » Sun Dec 31, 2017 6:10 am

There are two Carbs, the 2100 and the 2150. The 2150 is equipped with an electric choke. Yours is the 2100 and does not come equipped with a electric choke. It appears your 2100 is missing the cradle that the hot water lines rests into for proper choke operation. See the following pics. But this shouldn't be the cause of the issues you are having

A 2150 carb conversion is doable as far as I can see if you can locate the Red power wire as discussed at the following link.
http://www.ifsja.org/forums/vb/showthread.php?t=174411. You may have to source the connectors and wiring highlighted in green as detailed.

1979bettywhite · Post by **1979bettywhite** » Sun Dec 31, 2017 6:16 am

You are right on the cradle. I tried to see if this would help the issue by temporarily zip tying it to the cover. Still did not help. Seems the butterfly wants to hang about 3/4 open and not kick all the way open and the fast idle linkage wants to stay engaged. Even if I push it down with my finger, any throttle I then give it re-engages the fast idle cam.

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Driftwood · Post by **Driftwood** » Sun Dec 31, 2017 6:17 am

Curious, does your cruise control work? I wish mine did.

1979bettywhite · Post by **1979bettywhite** » Sun Dec 31, 2017 7:22 am

Mine does not.

letank · Post by **letank** » Sun Dec 31, 2017 3:07 pm

the throttle screw is the flat head one

from this one

http://theamcforum.com/forum/motorcraft ... 42497.html

and a full manual here, on the 5th post

http://theamcforum.com/forum/motorcraft ... 15645.html

Theamcforum is very usefull... almost same engine, carbs and trans

Driftwood · Post by **Driftwood** » Tue Jan 02, 2018 7:29 am

Here's a good article on carburetor rebuilds at HotRod Network.

Rebuilding the Autolite 2100/Motorcraft 2150 carburetor

Driftwood · Post by **Driftwood** » Mon Aug 24, 2020 8:42 am

Driftwood wrote: ↑Sun Dec 31, 2017 6:17 am Curious, does your cruise control work? I wish mine did.

I finally got my cruise to work! How are your carb issues coming along?

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