Car runs with mixture screw turned all the way down.

[Pete W]

Hi,

Is there always a vacuum leak if I can turn the mixture screw all the way down and the car still runs? I have a situation where the car stalls at a stop sign and I started messing with the carb and bungled everything up. I'm hoping it's not a vacuum leak and I can just "adjust" my way out of the situation.

Holley 1908 one barrel with auto choke

 

[The Plankster Prankster]

there are 2 main reasons why that can happen.
1) vacuum leak, as you suspected. only a probably suspect if the engine is running too lean, which by the sound of it, "turned all the way down" you're trying to lean it out cause it's running too rich, am i correct? if so, a vac leak is not your problem
2) your carb is wearing out. ALL carbs, when they wear out, will run either too lean or too rich. and all the adjusting in the world won't get around it. in my truck, i can unscrew (lean out) the idle screw until it falls out in my hand, and it runs better and better until it falls out. that carb's just worn out and there's nothing to be done for it, except replace the carb.

do you know wether you're running too lean (not enough fuel) or too rich (too much fuel)?

 

[Bort62]

Carb running w/ idle mixture screw bottomed out = running of the main circuit.

It means that your throttle plate is open too far, past the transfer slot.

If there is nothing wrong with your idle circuit, you should be able to set the idle screw back 1.5 turns or so and then close the throttle plate sufficiently that it resumes running on the idle circuit and not main circuit.

If you have problems w/ the idle circuit or other parts of the carb, it's possible that you won't be able to get it to run on the idle circuit w/o fixing it.

 

[66 Fastback]

Ditto what Bort said. Depending on what manuals you look at the throttle stop might also be refferred to as the curb idle adjustment screw or just the idle speed adjustment screw.
Doug

 

[kuhlou]

is there a place to go for carb manual reprints online? specifically looking for autolite 1100 and hw 5200.

 

[james singleton]

PeteW, I had the same problem as you are experiencing with a new/rebuilt carb that I had purchased. When I first installed my carb (a Autolite 1100) I had started with the fuel mixture screw out 1 & 1/2 turns, but it did not want to keep running without me adjusting the idle (with the idle adjustment screw; "NOT" the fuel mixture screw) above the called for idle rpm's. Like yourself, when I screwed in the fuel mixture screw all the way it did not seem to make a difference; the engine would not die like I expected it to; and the engine was running rough! What I found out later was that my particular carb (off of a 63'Fairlane) called for an initial setting of the "fuel mixture screw" to be turned out between 3 & 4 turns. By turning the fuel mixture screw between 3 & 4 turns, and having my idle adjustment screw closer to the called for idle rpms (650 rpms or so), or throttle plate closed more in the position it should be in, my carb worked just fine. Hope this helps. I believe this is part of what Bort62 is saying in his post, just a different way of putting it I believe??? Good Luck! Jim

 

[jahearne]

The 1908 are just like the 1904 and 1960 models.

http://www.carburetorfactory.com/expvw11.html

There's no transfer slot that I can tell.

http://www.oldcarmanualproject.com/manu ... /index.htm