Autolite 4100 tuning

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?

mustang808 said:

The advance is set at about 800...

Click to expand...

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

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.

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