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Old 12/29/11, 05:09 AM   #1
f2502011
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Motorcraft 2100/2150 Mixture Screw Adjustment?

I've searched and found a few different recommendations for adjusting the two mixture screws on the front of the carburetor. What's the best/easiest/simplest way or method to get it tuned right?
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Old 12/29/11, 05:18 AM   #2
turbotim2
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I usually start at 1-1/2 turns out from seated then adjust from there along with the idle. Where are you starting from? Was this a rebuilt carb or are you just trying to readjust your carb in its existing condition? I like to start but making sure the floats and butterfly valves are properly set and the choke is working correctly.

77 Bronco without fuel doors.
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Old 12/29/11, 05:22 AM   #3
f2502011
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Quote:
Originally Posted by turbotim2 View Post
I usually start at 1-1/2 turns out from seated then adjust from there along with the idle. Where are you starting from? Was this a rebuilt carb or are you just trying to readjust your carb in its existing condition? I like to start but making sure the floats and butterfly valves are properly set and the choke is working correctly.
I rebuilt the carb yesterday. Everything is set right. Only thing I am unsure about on the adjustment are the mixture screws. I put the mixture screws exactly where they were before as I counted how many turns to remove. It runs fine, maybe a little on the rich side, but I think it could run a bit better and would like to fine tune.
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Old 12/29/11, 06:13 AM   #4
f2502011
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On the bottom of the carburetor near the right mixture screw (one on driver's side, right side facing carb from front of engine) there is a port on this carburetor that has been plugged off with vacuum hose and a stopper in the end. Any idea what this port is for and where it is supposed to hook to? Is this a vacuum port?
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Old 12/29/11, 06:25 AM   #5
turbotim2
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Do you know if it is a 2100 or 2150? I have the 2100 and there is no port on the driver's side of the carb. I have a pic if you want to PM your email address.

77 Bronco without fuel doors.
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Old 12/29/11, 08:24 AM   #6
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Hook up a vacuum guage and adjust the screws to get the highest steady vacuum reading. adjust both screws the same amount to keep them even. adjust the idle speed to 700 rpm in neutral. You will have to adjust the idle speed as you adjust the mixture screws.
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Old 12/29/11, 12:01 PM   #7
f2502011
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Do you know if it is a 2100 or 2150? I have the 2100 and there is no port on the driver's side of the carb. I have a pic if you want to PM your email address.
The id on the choke says 2100. The sticker that was on the plate is gone. I think it's a 2100. Came with California emissions so maybe the extra port has to do with that?? I found a picture of the same carb online on a jeep and it said EGR or vacuum advance. I'm going to hook it back into the vacuum tee and see what happens.
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Old 12/29/11, 12:07 PM   #8
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Yea, it may very well have to do with the CA emissions stuff. The advance port is on the passengers side on mine.

77 Bronco without fuel doors.
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Old 12/29/11, 12:24 PM   #9
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Normal Bronco carbs had 2 vacuum ports for the carb on the smog models. One on the passengers side and tee-ed into the egr the vacuum timing amplifer module and to temperature sensors then to the vacuum retard side on the side of the advance cannister. This is straight manifold vacuum at the carb. The other vacuum connection was under the float bowl on the driverside and that is hooked up to the end port on the vacuum cannister for vacuum advance. There should be little to no vacuum on this line at idle.
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Old 12/29/11, 02:32 PM   #10
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Quote:
Originally Posted by rustytruck View Post
hook up a vacuum guage and adjust the screws to get the highest steady vacuum reading. Adjust both screws the same amount to keep them even. Adjust the idle speed to 700 rpm in neutral. You will have to adjust the idle speed as you adjust the mixture screws.
exactly! X2!!!

'75 Bronco- 3.5" Super Lift, 35" Goodyear MTR, NP 435, Detroit rear, 4.11's, 9500# winch, Taurus fan, Carter 4070 fuel pump, Magnaflow exhaust
'84 Bronco II- 4" Skyjacker Class II lift, Bushwacker flares, 35" M/T's, Autolite 2100 carb, 3 core radiator, 4-pt roll cage, 8.8" rear
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Old 12/29/11, 04:09 PM   #11
f2502011
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Quote:
Originally Posted by Rustytruck View Post
Normal Bronco carbs had 2 vacuum ports for the carb on the smog models. One on the passengers side and tee-ed into the egr the vacuum timing amplifer module and to temperature sensors then to the vacuum retard side on the side of the advance cannister. This is straight manifold vacuum at the carb. The other vacuum connection was under the float bowl on the driverside and that is hooked up to the end port on the vacuum cannister for vacuum advance. There should be little to no vacuum on this line at idle.
This sounds like the info I need but I'm having a hard time visualizing it. Do you know where I could find a diagram or picture that may show the routing? On mine there is a tee that has 3 ports coming out of it on the front of the engine on top of where the upper radiator hose connects to the engine. Bottom port goes directly to the vacuum advance on the distributor. Middle port goes to air cleaner and to another tee also on the front of the engine that runs to the back of the engine and also back into the main intake vacuum source tee. Top port goes to right (passenger) side of carburetor.
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Old 12/30/11, 01:57 PM   #12
YNOTBOB2007
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Is one screw for fuel and one for air? My passenger side screw I was told is for the air and is adjusted out considerably more...by 3 turns or so then the drivers side screw (this is what gives the highest rpm). If I adjust the 2 screws the same, it runs rough. I'm adjusting at 2500' elevation & someone told me they will be different at a higher elevation. This is a rebuilt 77 carb.
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Old 12/30/11, 02:28 PM   #13
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They are both fuel. 1 for each throat of the carb. Run both screws all the way in softly. back both out 1 and 1/2 turns. start the motor, choke off and engine warm and turn each scres in 1/4 turn at a time keeping them both the same. The engine will start to speed up and still run smoth. stop there. If you have a vacume guage Post 10 is better. I seldom get the vacume guage out. You are adjusting the fuel the engine gets at idle.
Thw high speed jets are taken care of by the size of the jets in the carb
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Old 01/05/12, 03:40 AM   #14
f2502011
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Quote:
Originally Posted by Rustytruck View Post
Hook up a vacuum guage and adjust the screws to get the highest steady vacuum reading. adjust both screws the same amount to keep them even. adjust the idle speed to 700 rpm in neutral. You will have to adjust the idle speed as you adjust the mixture screws.
Where is the best place to hook up a vacuum gauge to do this?
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Old 01/05/12, 04:22 AM   #15
turbotim2
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You will want to tap into the manifold vacuum, off the tee behind the carb is a good place to do this.

77 Bronco without fuel doors.
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