Idle screws have no effect

[gip63]

 I have a edlebrock 1411 and noticed idle screws have no effect even if you close them down. I took it apart and cleaned it good and reinstalled it, same thing.  It's funny it idles fine and seems to work fine other than that. I can't find a vacuum leak but it has been running rich a I'm wondering if that's part of the problem. Any ideas about this?

[odzking]

I have an older AFB that has one side like that. I'm told it is clogged somewhere. But I have never had time or $$ to have it taken care of. It is my spare so I kind of forgot about it frankly.

[Deleted]

3 things come to mind. Vacuum leak, plugged up carb, which you seemingly have addressed.
The other thing... throttle plates open far enough that carb is not running on the idle circuit, it's running on cruise circuit.

[DynoDave]

Mar 25, 2015 22:33:01 GMT -5 gip63 said:

I took it apart and cleaned it good...

I don't know if this will help or not, but I'll mention it.

When I took a fuels class in college, our instructor was a gentlemen who owned his own shop, and had a reputation around town for being able to diagnose problem vehicles.

Of the things he taught us when rebuilding a carb, was to "chase" EVERY passage in the carb. Over time I've used carb cleaner with it's red "straw" to do this. He preferred cigarette smoke (he'd disassemble the every-present clicker-style ball point pen in his pocket, and use the non-clicker tube end like a straw, and blow cigarette smoke through every passage). I've seen others use a fine piece of wire, though I've personally had less luck with that.

Just wanting to make sure that when you say you cleaned it, that the cleaning included manually checking every passage in some way.

[gip63]

Well when I cleaned it I used carb cleaner, high pressure air and tooth brush. I haft to say I can't figure out how that thing works as far as how fuel moves through the carb but to me using smoke is interesting to find out. I called a tech at edlebrock and he said check fuel pressure and clean it but all in all not very helpful really. 

[DynoDave]

If you used carb cleaner and air, and had good flow through all the passages, you should be good in that respect.

I've run into folks that skip this step, just soak the carb, and assume all is good. Glad to hear that's not the case here.

[Deleted]

Another thing to add...though I have never experienced this before first hand.
I have read multiple times about people having problems with brand new Edelbrocks, straight out of the box, due to casting flash obstructing passages.

[71se3834v]

Mar 26, 2015 13:35:53 GMT -5 @tom said:

The other thing... throttle plates open far enough that carb is not running on the idle circuit, it's running on cruise circuit.

I'll 2nd this.
Make sure your basics are correct. It is possible to not have enough advanced timing to cause slow idle. Then you have to increase the idle screw to get the rpm's up which will open the throttle plates causing fuel to be pulled from the intermediate circuit or the venturi.

One other possibility....
Take a look down your carb while it's idling to see if fuel is dripping from the venturi. Fuel level too high (misadjusted floats) will cause fuel to drip out at idle and therefore closing the mix screws will have no effect.

[gip63]

I guess fast idle could be set so high as to cause it to run on main curcit also right? Casting metal is present in some places but this carb did work right not long ago. I like the simplicity of this carb and I bet we get it going shortly. Tomorrow it should be warm outside and after church ill look into the things mentioned and see what I can find out. The back firing seems to have cleared up when I put new plugs in, running rich like it did fouled the old ones out. 

[Deleted]

Mar 28, 2015 20:09:38 GMT -5 gip63 said:

I guess fast idle could be set so high as to cause it to run on main curcit also right?

Yes