Autolite 4100

notny41

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Aug 15, 2004
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First of all, I want to say thank you to everyone! I have received a tremendous amount of help on all of my Mustang questions. This is a great resource!

I was wondering if anyone has any links or information on the Autolite 4100 carb.

Specifically which of the two screws on the front of the carb are for idle mixture and which is for high-speed mixture.

Also, I don't know if you can tell much about the color of the plugs insulators, but I pulled one last night and the insulator was just about all white. Had just a small bit of yellow on it. No deterioration of the electrodes that I could tell though.

I have a 289 that runs a bit rough (like it is missing or something) while going down the road most of the time.

Thanks - Paul
 
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67stangvert

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Pony Carbs

I had my 2100 done by Pony Carbs and my 4100 done by Pony Carbs. Their website is useful. Do a search for Pony Carbs. Any time I have called with a question, they have answered it for me.
 

302 coupe

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I don't believe there is a so called high speed mixture screw. Fuel mixture above idle speed is controlled by the jets. The screws on the carb body are to adjust idle mixture for each front barrel, respectively.
 

Ozsum2

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Try the Ford Shop Manual. It has COMPLETE info for all carbs used by ford on stangs.
 

notny41

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Thanks 302!

Then it would stand to reason that they should both be backed out an equal number of turns - correct?

P
 

Ozsum2

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notny41 said:
Thanks 302!

Then it would stand to reason that they should both be backed out an equal number of turns - correct?

P

Idle mix screws can vary as much as 3/4 turn.
 

JB66

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If you have access to a CO meter, it would help. On mine, I turn the screws clockwise until fully seated (do not tighten!), Then start with 1 3/4 turns counterclockwise for a preliminary setting. Adjust as needed on both screws for a good idle.
 

bnickel

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Ozsum2 said:
:D :rlaugh: :lol: :lol: :lol: Yea right. I use a vacumm gauge and or a tach.

i use all of the above. i adjust the idle and timing initially with a vacuum guage and the tach and fine tune it by ear, after all a vacuum guage can't hear a slight sound difference between the left and right bank and also can't hear a slight ping when the engine has a good load on it like accelerating up a long hill in third gear :D
 

Ozsum2

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bnickel said:
i use all of the above. i adjust the idle and timing initially with a vacuum guage and the tach and fine tune it by ear, after all a vacuum guage can't hear a slight sound difference between the left and right bank and also can't hear a slight ping when the engine has a good load on it like accelerating up a long hill in third gear :D

I agree. Also, a slight ping under the conditions you discribe is a good thing. No ping wouldn't be enough. You jusst don't want a ping under normal everyday driving.
 

notny41

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Well, a previous owner had the screws backed out as follows:

Driver side bank: 2 1/2 turns
Passenger side bank: 1 1/2 turns

With these settings I had to pump the gas pedal 5 times and then once the engine fired up I had to keep pumping the pedal every second or so to keep the engine running.

I got the thing to idle without pumping the gas at:

Driver side bank: 3 3/4 turns
Passenger side bank 3 3/4 turns

Does that seem like it would be too rich?
 

notny41

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OK wait a minute...

So the idle mixture screws will change how your car runs when it is pulling a load? I thought they are just for idle???
 

302 coupe

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the mixture screws are just for idle, I don't know how Oz and bnickel started talking about pinging under load in relation to adjusting the mixture screws.


notny41, be sure the engine is at full operating temp before adjusting the mixture screws. It sounds like you might have a choke adjustment problem. I ran a chokeless carb for a while on my car and in the winter I just richened up the idle mixture with the mixture screws to compensate for the lack of enrichment normally provoided by the choke. Having the screws turned out as much as you do is putting in a lot of gas at idle. If the engine was warm when you set them at 3 3/4, you may have another problem. What is your initial timing? Keep in mind that the 4100's only have a full time vacuum port and must be used with the proper distributor, or a mechanical advance only distributor.
 

notny41

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I would say that the engine was rather cold when I set those screws. I'll check the timing again tonight now that I can see the timing lines. I do have a vaccuum advance on my distributor. Should I disconnect that? It was disconnected when I initially got the car (the vaccuum line was just laying on top of the intake manifold with no plug in the end of it).
 

302 coupe

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If it were me....(with a warm engine)I'd disconnect the vacuum advance and plug the line. Hook up the timing light, start the engine, set idle to 800 rpm, timing should be at a steady 12 degrees or so. Then I'd try to turn the idle mixture screws in some, normally I just turn them in until the rpms drop start to drop off, then back off a half turn. Once that is done, re-connect the vacuum advance on your dizzy and re-check your timing. I would imagine that is at about 22-24 degrees at idle which is too much. If you have the right dizzy, you'll be able to leave the vacuum advance connected to get 12 degrees at idle, then still only be at 33 or so by 3000 rpm. Chances are the dizzy is the wrong one though. Write back with the results and we'll go from there.
 

Ozsum2

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302 coupe said:
the mixture screws are just for idle, I don't know how Oz and bnickel started talking about pinging under load in relation to adjusting the mixture screws.


notny41, be sure the engine is at full operating temp before adjusting the mixture screws. It sounds like you might have a choke adjustment problem. I ran a chokeless carb for a while on my car and in the winter I just richened up the idle mixture with the mixture screws to compensate for the lack of enrichment normally provoided by the choke. Having the screws turned out as much as you do is putting in a lot of gas at idle. If the engine was warm when you set them at 3 3/4, you may have another problem. What is your initial timing? Keep in mind that the 4100's only have a full time vacuum port and must be used with the proper distributor, or a mechanical advance only distributor.

Because b said he used his ear also to set the timing. Read his post. :rolleyes: If he needs to have the idle screws out that far, he needs to check the choke, and I'll just bet with all that pumping, the fast idle cam isn't working properly. Ideally, he needs 1 pump to set the choke and that in turns lets the engine idle at the prescibed rpm until it starts to warm up. You with me? :shrug:
 

302 coupe

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302 coupe said:
... be sure the engine is at full operating temp before adjusting the mixture screws. It sounds like you might have a choke adjustment problem....
I was with you before you even knew it....
 
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