carburetor wont adjust

[edhCO]

So... I am tuning my carburetor. The idle has been at 1300 RPM
I checked for vacuum leaks...none.

I can screw the idle mixture screw all the way in, and turn the idle speed screw all the way in, and fast idle is the same. No change in RPM

I cant get this baby to settle down to the 700 I am looking for.

FYI the Solenoid cut off was not connected before. now it is.

Anyone had this problem before?

Vacuum is pulling 16"

 

[Pin_Head]

I assume that this is a stock '75 carb. Chances are you have not found the real idle speed screw yet. It in the base of the throttle body casting between the primary and secondary shafts. Get the idle speed down to about 650 and then you can set the idle mixture. There is the fast idle screw which sets the speed with the choke on and there is the throttle positioner speed screw, but these are on the linkage and not part of the carb base.

 

[dgangle]

If Pinheads suggestion doesn't work, I suspect a vacuum leak...yea, yea I know you said none but...

spray carb cleaner around the carb/intake and see if the idle speed increases. If so you gotta leak. Also remove the brake booster vac line and plug. If this helps you gotta bad booster and without fixing this will surely result in a burned #5 intake valve in your immediate future.

 

[edhCO]

I'm sure I have the right idle mixture screw.
it doesn't seem to make a difference.?

 

[Pin_Head]

I'm sure I have the right idle mixture screw.
it doesn't seem to make a difference.?

I'm talking about the idle SPEED screw. The idle mixture screw will have no effect with the throttle open and it running off the main nozzle.

Also: maybe the linkage is stuck so the throttle plate can't close completely. Take the air cleaner off and take a peek. There should be no gap betwen the brass butterfly and the throttle body bore with the idle screw backed out all the way. Check the linkage and things like the vaccum throttle positioner and its linkage to make sure that something isn't hanging it up.

 

[inkpot]

I'm sure I have the right idle mixture screw.
it doesn't seem to make a difference.?

Howdy! You mentioned that the idle speed solenoid was not working before. I would guess that someone buggered the idle settings to get it to run this way. Besides the idle SPEED adjustment, they may have messed up the choke linkage that also raises up the idle speed when the engine is cold. John

 

[edhCO]

I think the linkage is boogered.
Image shows idle SPEED screw All the way backed out.

What do you see?

Looks like the linkage is bent so the butterfly wont close completely.... before i bend this, do you agree?

 

[Pin_Head]

That would be the throttle positioner speed screw, not the main idle speed screw.

The main idle screw passes through the cast iron base at the bottom of the carb behind the linkage. You can see it in this picture where it is partially obstructed behind the vertical spring.

 

[edhCO]

I do not have that screw, instead it has a screw that is approx 3" and is horizontal to the ground and in line with the axels. (not a '75?)

I have backed it out, but the butterfly doesn't drop with it. There is an adjustable linkage from the accelerator pedal which may be preventing it from it's full range of motion.

What do you think? Thanks for your help Pinhead!

 

[Pin_Head]

There are 3 screws, but only one is the main idle speed screw. It is hard to see and I don't think you have seen it yet. You have to get in there with a flashlight to see it and it is hard to get a screw driver on it.

 

[edhCO]

got it... it's down @ 700!
Thanks!