[mustang808]

Hey guys, I have a 66 289 with an Autolite 4100 and trying to set the fuel/air mixture. Has anyone experienced that even with the screws all the way in they engine will still run and not stumble? The advance is set at about 800 and with the vacuum advance off.

 

[Ivy66GT]

Your primary or secondary throttle plate is/are probably open to far and the car is not really running on the idle circuit but gettings its fuel through the main jets. The adjustment screws only control fuel through the idle circuit. If it idles with those closed then your fuel is coming from somewhere else; main jets, leaking power valve, etc.

Either that or your idle is so fast that you aren't using the idle circuit at all. What is your idle speed?

The advance is set at about 800...

I am not sure that that means. Advance is measured in degrees.

 

[mustang808]

Your primary or secondary throttle plate is/are probably open to far and the car is not really running on the idle circuit but gettings its fuel through the main jets. The adjustment screws only control fuel through the idle circuit. If it idles with those closed then your fuel is coming from somewhere else; main jets, leaking power valve, etc.

That what I was thinking, the car sat for about 7 years in my brothers garage before I bought it from him. I did pull the carb to see if any of the butterflies were stuck open but were all shut. Guess I'll have to overhaul the carb to make sure and clean out all that ethanol residue, etc.

Thanks Ivvy

 

[Ivy66GT]

Usually today's gas evaporates with nothing left at all. Any stickiness that might be there is the fuel itself and nothing to do with ethanol. We had gummy carburetors decades before ethanol came into use. From what I see, that problem was much worse before we had ethanol.

Provided your needles are seating and closing off the idle passage you are getting fuel at idle from some other source. You just have to find from where.

 

[Veronica]

Hello. One thing to look at while you have the carb off would be the condition of the little holes that the idle air/fuel adjustment screws seat into. Sometimes people get the idea that 'run the screws all the way in until they are seated, and then back them out a turn and a quarter' means to tighten those screws until you have nearly stripped the threads. If the guy down at Magilla Automotive has worked on this carb, it could be that those holes are all beat up and it is not possible for the needle to seal the hole.

 

[Ivy66GT]

Agreed, that's what I meant by "Provided your needles are seating..." Not only can you wreck the seat but also wreck the tip of the needle.

If the thread and seat in your carb body is still intact, you can buy a new needle for $5. Even get your choice of styles.
The needle for a 2100 and a 4100 are the same, just there were several different styles of them for either carb.

Style 1

Style 2

These people offer NINE different styles although prices vary considerably.

https://buy.walkerproducts.com/carb...d-2bbl-2100-2150-1-carburetor-components.html