My truck suddenly started having a rough idle when warmed up. It chokes fine, but once it is up to full temp, it runs rough and wants to stall. I have done a carb kit on it and checked vacuum lines. I have tried the mixture screws but doesn't help to much. No emissions items hooked-up. As soon as you close the choke plate or step on it, the idle smooths out. So it seems to be not getting enough fuel at idle. Anybody got any ideas?

 

Does turning the idle speed screw in help it smooth out at all?

 

Adjusting the idle screws really doesnt effect it to much. It speeds up slightly but still is rough.

 

[font size="1" color="#FF0000"]LAST EDITED ON 30-May-01 AT 03:47 PM (EST)[/font][p]Hi,

How is everything else on the motor? Are the plug wires and cap/rotor OK? Are the plugs OK, or are they fouling once warmed up? How is the coil, is it breaking down when hot?

Also, how much vaccum do you have at idle? Should be aroung 20" of HG. How is the vac advance for the distributor, is it wired up ok? Where is the timing set?


Some things to look at..

-Brents

 

Look under the carb. Is there an EGR spacer plate in there with the diapham hanging off the back. Is the spacer aluminum? Ford made a ton of money selling replacement egr spacer because the aluminum ones get eaten up internally. Only causes problems at idle or slow cruise (surging). Just a thought.

1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

It has a steel egr spacer. Timing is good. Vaccuum is
about 15 and steady. Plugs and wires good.

 

Are the ports blocked off to the egr? (I assume you do not use the egr?). If not, the egr may be leaking causing a rough idle.

 

Keelbar, if it idles OK when cold, and then idles rough when warmed up, I think you have a vacuum leak somewhere. Take another look at where the carb base sits on the spacer and the spacer sits on the manifold. The carb base could be a little warped, and everything is expanding enough to leak when it gets warm.
Don

 

 

I changed carb! Runs great!