Please explain the two screws in the front of the carb. I believe they adjust the fuel/air mixture.
My problem is this, the car is tempermental in starting. It sometimes needs fuel to stay running. In addition, if I am stopped at a long light it will die after about a minute. Finally, if you gun it off the line it struggles to keep up and chugs instead, accelerating gradually does not seem to be a problem. I believe the problem lies with the carb which has always been difficult. I have turned one of the lower screws and a screw on the right side with a spring around it if you are looking at it from the front.
Any advice would be greatly appreciated. Thank you I am eager to gain the skills to work on my car rather than always rush it to the shop.
The two screws in the front are to adjust the air/fuel mixture. You need to get the Holley Carburetor manual from Haynes (most auto parts stores carry it) and use it's instructions to tune the carburetor (I can't remember if they list the Autolite 2100, but it's mechanically similar to the Holley 2300, they even resemble each other strongly, and you can use those directions.) Also, you'll be better off using a test-tach than the factory tach for your adjustments, and while you're at it, check your ignition timing (you'll need a timing light if you don't have one.)
To get the carburetor's air/fuel ratio close enough to get it started fairly easily, do the following:
Screw in both of the front screws until they are snug.
Back out each 1 1/2 to 2 full turns (equally).
Check the idle speed screw(on the linkage to the carb) to make sure that the butterflies on the carburetor (the ones at the bottom, the top ones just do the choke) are just ever so slightly open (no more than the tiniest bit more than the width of a human hair, too little will just keep it from starting, too much can leave your engine free-revving from the instant you turn the key, possibly causing damage. If in doubt, turn this screw till they are closed, then try to start it, and each time it doesn't start, turn that screw in about 1/4 turn till it will start and run, then turn it in until it idles somewhat smoothly so you can start making your fine-tuning adjustments.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
After turning the mixture screws out equally from the snug position two full turns the car starts better and runs better stopped in drive. However it still died while in drive and a black spot is gradually created when in park after it is already running. I assume this to mean it is still getting too much gas. In addition it still gets behind and struggles when rapid acceleration. Which of the two mixture screws regulates gas or do I need to turn them equally in small increments to remedy the problem? Thanks
as far as the accelleration part there maybe a faulty accelleration pump, the idle problems could be the float is ether sticking or sinking from a hole in the surface of the float...
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06 Mustang GT
Performance White
06 Mustang V6
Windveil Blue
About the accelerator pump, could you describe where that is on an Autolite 2100 and how one goes about making sure it is set right? I do not really understand the internal working of a carb. is there a way to check the float without opening it all up.
None of my problems existed a week ago and all that has happened since is an adjustment to the mixture and a new fuel filter. The original concern was a dead spot as you accelerated. Once you drove through it everything was fine, as well as problems accelerating slowly up hill. I was told this may be the float but was also told it was a lot of work to open everything up and put it all back together. Thanks
check this Hope it helps...
In the first link the float is made of brass, It very common for them to get a hole in them causing the float to sink...
These carbs had/have a bad habit of boilover when they get hot pushing gas past the accel pump and into the engine causing a flooding like
simptom(hard starting)...
When adjusting them you need to turn them in equally in small increments, the position I described above was just a baseline to start from (as it's usually just a little to the rich side, but in the same ballpark, close enough to get the car started so you can adjust it properly.) You seriously need to get a good tech manual for the carb though, as it'll give you full troubleshooting info, and very detailed tuning info (I can tune a carburetor by ear and get really close, but if I go with the tuning specs in the manual for the carb in question it always gets the tiniest bit better gas mileage and/or accelerates just the littlest bit better.) The manual's all of $15-20 at an auto parts store, and will save you that much in gas in a month.
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1976 Ford Mustang II Ghia: 302 with a 600cfm Edelbrock carb, Edelbrock Performer 289 intake, Dynomax Blackjack headers, 2.5" exhaust with Flowmaster Super 44s. RJS 11-gallon fuel cell, C4 tranny, chrome 16" pony wheels, fuzzy dice, brown vinyl half-top, and painted in the tackiest color ever (harvest gold, that's why I call it "The Goldenrod").
Also have a 2003 Dodge Ram (lightly modded daily driver/tow rig/office/dining room/home away from home/workshop... I call it "The Big Blue Dawg".)
Hello.Many people classify understanding carburetors as a dark art, but it really isn't all that mystifying.Here's a capsulized version of how your 2100 does the things that it is supposed to do.The air/fuel mixture is pushed into the motor by three different circuits.The idle circuit is the one that is only working at very low rpm, closed-throttle situations.If you were looking at the bottom side of the carb, you would notice two small holes in the sides of the venturis.The two idle air/fuel mixture screws that you have been tweeking are pointing right at them.If you run those screws in all the way they would plug up those holes.You will also notice that they are underneath the throttle plates.Engine vacuum sucks fuel through these holes when the throttle plates are closed,but when the throttle plates start to open, fuel quits coming through there.If you open the throttle plates up some, you will notice more holes that became exposed as the throttle plates open.These are the discharge outlets for the transition circuit,which supplies fuel until the main circuit engages.The problem is that there is a slight lag in time between the time the idle circuit shuts down and the transition circuit begins operating.This is compensated for by the accellerator pump, which supplies a shot of gas immediately when you step on the pedal, and the power valve, which supplies a little more gas when engine vacuum drops because of the opened throttle plates which functionally created a big hole in the top of the motor.The main circuit operates when the throttle plates have been open a significant amount for a while.
All carburetors are basically self-powered, fully adjustable throttle body fuel injection units.The power source for them is the air pressure differential between the fuel bowl and the inner tunnel of the booster venturis(those two little tapered tube thingys in the middle of the barrells of the carb).A moving column of air is at it's highest velocity and lowest pressure at smallest part of tapered tube.That is why there is a vent on top of the fuel bowl.You have normal atmospheric pressure pushing on the fuel at one end and a greatly reduced pressure pushing at the venturi end, which causes the fuel to be pushed down into the moving column of air.This is why float level is so important.If the fuel level is too far below the discharge nozzles, the pressure differential won't be enough to push the fuel through.If the float level is above the discharge nozzles, that will cause the fuel to siphoned off when the car isn't running, making for some pretty hard starting, since the car has to refill the fuel bowl before it can start.
From what you describe it sounds as if the thing that you have been messing with is the only system on your carb that is actually functioning like it's supposed to. I think that if you go ahead and throw about 15 bucks at a rebuild kit and replace the accellerator pump diaphragm and the power valve, and then set the float level correctly, many of your issues will be solved.Hope that helps.
If the carb is mounted, how do you observe the gap? What settings should the cold start screw be in, the middle of three lobes? My 2100 autolite is a bear to start. I have the bimetalic spring two notches ccw and the butterfly choke acts like it should, but it still takes about 10 seconds of cold cranking to actually light off.
also check your accelerator pump diaphram. Your autopart store should carry it. if it has a slight hole or tear in it it will cause your car to die coming off the line like you described. Hope this helps.
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-Jared 1968 Coupe 289 4V.
What i've done...
-New steering box
-New interior
-Front end rebuild
-Disc brakes and brake system rebuild
-Edelbrock 4V
All at the age of 17
Autolite 2100 Carb trouble 
Many people classify understanding carburetors as a dark art, but it really isn't all that mystifying.Here's a capsulized version of how your 2100 does the things that it is supposed to do.The air/fuel mixture is pushed into the motor by three different circuits.The idle circuit is the one that is only working at very low rpm, closed-throttle situations.If you were looking at the bottom side of the carb, you would notice two small holes in the sides of the venturis.The two idle air/fuel mixture screws that you have been tweeking are pointing right at them.If you run those screws in all the way they would plug up those holes.You will also notice that they are underneath the throttle plates.Engine vacuum sucks fuel through these holes when the throttle plates are closed,but when the throttle plates start to open, fuel quits coming through there.If you open the throttle plates up some, you will notice more holes that became exposed as the throttle plates open.These are the discharge outlets for the transition circuit,which supplies fuel until the main circuit engages.The problem is that there is a slight lag in time between the time the idle circuit shuts down and the transition circuit begins operating.This is compensated for by the accellerator pump, which supplies a shot of gas immediately when you step on the pedal, and the power valve, which supplies a little more gas when engine vacuum drops because of the opened throttle plates which functionally created a big hole in the top of the motor.The main circuit operates when the throttle plates have been open a significant amount for a while.
I think that if you go ahead and throw about 15 bucks at a rebuild kit and replace the accellerator pump diaphragm and the power valve, and then set the float level correctly, many of your issues will be solved.Hope that helps.
