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Old 04-27-2004, 01:27 PM
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Another Motorcraft 2100 question.

OK, this might be the dumbest question in the world, but both idle mixture screws control the amount of gas going into the engine correct?.....i ask because some random guy in my autoshop class said that one screw is for air, the other is for fuel. So whos right?.........anyone who can clear this up for me once and for all will be greatly appreciated.THANKS AGAIN.

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Old 04-27-2004, 02:33 PM
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Arrow

Each screw controls the idle mixture fuel ratio of the venturi it is assigned. In and out adjustment will make the ratio leaner/richer.
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Old 04-27-2004, 02:40 PM
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Then what would be a good starting point for adjustment on a 351C 2V motor?.......i think i have it running at 2 3/4 turns out on each right now.......any suggestions will be appreciated as usuall
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Old 04-27-2004, 03:02 PM
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Yes, on that wacky holley design each one controls a seperate air/fuel mix for that barrel. This is why those (#*$(*!@)! carbs are so hard to tune, at least for me anyways. They say there is a fast idle adjustment screw on the pass. side, but it is so hard to tell if it even does anything on those carbs. Basicly work with the mixture screws until you get a good "low" idle in drive and then move on to the fast idle screw. At least thats how I do it.

The other wacky thing about it is they arent just idle mixture screws, they seem to control the primary mixture, so giving it a decent idle means you bog down when in drive and step on the gas?!?

I has to turn them outwards about 1 3/4 turns to get it to crank over.

For a REALLY cool effect, turn both screws out about 2 1/2 turns, back away, and step on the gas REAL hard! Makes pretty flames
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Old 04-27-2004, 03:17 PM
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The two idle mixture screws do just that. Adjust each one until you get the smoothest, fastest idle (with the engine hot, choke off). You may have to go back and forth between the two once or twice. The fast idle screw only works when the choke is on (imagine that!) and is on the same side of the carb as the choke thermostat. The curb idle screw is not to be confused with the fast idle screw, it's on the other side of the carb. The curb idle screw is what you use to set the idle speed with when the choke is off. You may need to re-adjust it after you get the mixture screws right.

tom
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Old 04-27-2004, 03:21 PM
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where is this curb idle screw, heard of it, but the 2150 here, doesnt seem to have it.
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Old 04-27-2004, 03:27 PM
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Quote:
Originally posted by 87442lover
where is this curb idle screw, heard of it, but the 2150 here, doesnt seem to have it.
It's on the throttle lever, it's called the "solenoid off (tsp off) idle speed adjusting screw."

tom
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Old 04-27-2004, 04:45 PM
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Ah yeah, I see them, there is actually 2 or 3 screws (electronic idle solenoid) on a throttle plate next to the throttle lever, one is stuck in place. POS!
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Old 05-16-2011, 10:18 PM
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Can someone answer this question,

I just got a rebuilt 2100D carburetor and it is not working right.
Here's the problem. It idles way too fast. The timing is set right, The throttle is not the problem. The fuel mixture screws when screwed all the way in, makes no difference at all the engine stays the same.
On the old 2100 carb, there was a vacuum port on the front of the car with little vacuum until you gave it gas. This car does not have a vacuum post on the front but it does have it on the passenger side with a lot of vacuum without giving it any gas.
So why do the mixtures screws not work right?
Do I have a bad rebuilt carb?
Email me jdcron@wmis.net
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Old 05-16-2011, 11:26 PM
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Quote:
Originally Posted by jdcron
I just got a rebuilt 2100D carburetor and it is not working right.
Here's the problem. It idles way too fast. The timing is set right, The throttle is not the problem. The fuel mixture screws when screwed all the way in, makes no difference at all the engine stays the same.
On the old 2100 carb, there was a vacuum port on the front of the car with little vacuum until you gave it gas. This car does not have a vacuum post on the front but it does have it on the passenger side with a lot of vacuum without giving it any gas.
So why do the mixtures screws not work right?
Do I have a bad rebuilt carb?
Email me jdcron@wmis.net
Might have been better to have started your own thread instead of reopening two different old threads, and replying via email isn't how we do it- that will render any replies useless to the masses who use a search engine for help.

With that out of the way, you need to adjust the curb idle screw to lower the idle. If the curb idle screw isn't lowering the idle, you either have a massive vacuum leak, the timing is over advanced or the fast idle cam of the choke is holding the throttle blades open too far.

The vacuum ports are either ported (no or little vacuum at idle, w/vacuum above idle) or manifold vacuum (vacuum all the time). Usually the factory used ported vacuum for the distributor vacuum advance during the smog years. Manifold vacuum is used for the power brake booster, vacuum modulator and the vacuum advance for some performance applications. If you use manifold vacuum for the vac. adv., the idle will be higher than if you use ported. This can usually be countered by dropping the idle speed using the curb idle screw.
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Old 05-17-2011, 04:33 AM
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2100 Motorcraft Carb

cobalt327, Thanks for this reply. I really wanted to start my own thread but, dang it, I forgot how to get to the "post".
Ok I understand what you are saying here.

I have my distributor vacuum going to the passenger side carb. It is sucking vacuum and when I pull the vac hose off from the distributor, the idle goes down to I think a normal speed but when I attached it again it idles why to high.
The idle screw on the carb throttle is out making no contact. The cam screw I had turned out all the way. The throttle plate doesn't open all the way either.
I will check for a vac leak here in just a little while.

I should mention that this 2100 2 brrl carb is setting on a Eldebrook intake. I have a spacer on it so the 2 brrl works on it. Maybe I do have a leak because of that..
Thanks for the advice. Any other will help. And tell me how to post and I will use that for the future.
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Old 05-17-2011, 06:50 AM
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Quote:
Originally Posted by 87442lover
Yes, on that wacky holley design each one controls a seperate air/fuel mix for that barrel. This is why those (#*$(*!@)! carbs are so hard to tune, at least for me anyways. They say there is a fast idle adjustment screw on the pass. side, but it is so hard to tell if it even does anything on those carbs. Basicly work with the mixture screws until you get a good "low" idle in drive and then move on to the fast idle screw. At least thats how I do it.

The other wacky thing about it is they arent just idle mixture screws, they seem to control the primary mixture, so giving it a decent idle means you bog down when in drive and step on the gas?!?

I has to turn them outwards about 1 3/4 turns to get it to crank over.

For a REALLY cool effect, turn both screws out about 2 1/2 turns, back away, and step on the gas REAL hard! Makes pretty flames
You must be talking about something else, not a 2100. They are about the simplest carb to work on and tune.
On most carbs, 1 1/2-2 turns is a good starting point.
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Old 05-17-2011, 12:25 PM
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Quote:
Originally Posted by jdcron
cobalt327, Thanks for this reply. I really wanted to start my own thread but, dang it, I forgot how to get to the "post".
Ok I understand what you are saying here.

I have my distributor vacuum going to the passenger side carb. It is sucking vacuum and when I pull the vac hose off from the distributor, the idle goes down to I think a normal speed but when I attached it again it idles why to high.
The idle screw on the carb throttle is out making no contact. The cam screw I had turned out all the way. The throttle plate doesn't open all the way either.
I will check for a vac leak here in just a little while.

I should mention that this 2100 2 brrl carb is setting on a Eldebrook intake. I have a spacer on it so the 2 brrl works on it. Maybe I do have a leak because of that..
Thanks for the advice. Any other will help. And tell me how to post and I will use that for the future.
No problem. To start a new thread, click on "Bulletin Board" at the top of the page. Then select a forum that matches your question (Engine, Tranny, Suspension, etc.) and click on it. Then at the top left side of that page you'll see "New Thread". Click on that and you're there.

After you look it over for vacuum leaks (you did use gaskets between the intake and the adapter and the adapter and carb, right?), is there any chance the adapter is causing the throttle blades to hang up?

That carb should have a ported vacuum port for the vacuum advance on it somewhere. If the piece of tubing pulled out of the carb, there may be nothing but a hole left, so look it over real good.

And the timing has to be set correctly. If the initial timing (timing at idle) is too high, the idle speed can also be too high.
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Old 05-17-2011, 12:58 PM
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Tuning Carburetor

OK here is what I have found.
Yes I did put a gasket on the intake and in between the carb.
So I decided to take off the Eldebrrok and put on the stock intake.
When I took off the intake, I saw the front rubber gasket was torn, and I think that was causing a vac leak. Also I had a LOT of fuel under the intake. The carb gasket as well as the spacer was wet with fuel. Not sure what cased this??? I do know it isn't suppose to be wet like that.
So I have to wait til tomorrow to get my valley pan and gaskets to put the stock intake on. We will see how it fires up then. I will let you know.
Any ideas on all the excess fuel???
Oh yeah I see on the carb I took off that the bottom butterflies were not opening all the way.
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Old 05-17-2011, 02:18 PM
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Quote:
Originally Posted by jdcron
OK here is what I have found.
Yes I did put a gasket on the intake and in between the carb.
So I decided to take off the Eldebrrok and put on the stock intake.
When I took off the intake, I saw the front rubber gasket was torn, and I think that was causing a vac leak. Also I had a LOT of fuel under the intake. The carb gasket as well as the spacer was wet with fuel. Not sure what cased this??? I do know it isn't suppose to be wet like that.
So I have to wait til tomorrow to get my valley pan and gaskets to put the stock intake on. We will see how it fires up then. I will let you know.
Any ideas on all the excess fuel???
Oh yeah I see on the carb I took off that the bottom butterflies were not opening all the way.
Definately not supposed to be fuel like you described. It could be the float adjustment, there could be debris causing the needle valve to hang open, the float could have a leak or be heavy, causing the float level to be too high or the fuel pressure can be too high.

But whatever it is, it HAS to be corrected or the excess gasoline will wash the cylinders clean of oil and that's the end of the rings and bores.

The front gasket/seal shouldn't cause a vacuum leak, but the intake gaskets can leak if there's a problem w/how they were installed. The surfaces have to be clean. I use sealant around the water cross over ports, but generally I don't use anything around the intake ports unless the instructions say otherwise. I will use weatherstrip cement in a few spots just to hold the gaskets firmly in place but this isn't supposed to seal anything- just hold them so they don't get bumped out of position when the intake is lowered into place. Edelbrock says to use their Gasgacinch sealant P/N 9300, it does the same thing- hold the gasket in place.

For the end seals, you can use silicone or "Right Stuff" instead of fooling around w/the gasket pieces. You can use the info HERE, under "INSTALLATION INSTRUCTIONS" to see how to install the intake and how to seal the ends. Use the pattern shown.
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