High idle, secondaries not closing after driving, why?

[Shawn MacAnanny]

I've finally got the A/F perfect, timing perfect and now the only thing bothering me is the idle speed. It's idling at about 800-900rpm sometimes as high as 1000. I want this down to around 600-700. I have the primary screw backed all the way out. I can move the secondary linkage to make the secondarys full close and the engine will die So i know that they are not fully closing. How do i make them close?



I do not have an intake leak as i am using an LS1 engine and their o rings do not leak I dont think that it is my PCV system with catch can. The carb baseplate is not leaking. I recently rebuilt the carburetor i have just always had this problem. What can i do to fix the secondaries not closin though? I sprayed some pb blaster on the linkage and such. I have the long yellow spring in it. There wasnt a check ball in the diaphram when i got the carb so i put one in it. What's causing them to stick open though?

[Shawn MacAnanny]

Ive read somewhere that i need to "re-bend the closer link", what is this exactly and how is it done?

[Mommy Wagon]

Did you adjust your throtle blades while you rebuilt your carb?

I am assuming it is a Holley (or Barry Grant, Demon, AED, etc), if it is not let me know.

If your primary throttle blades are set at a specific opening, your idle screw will be useless lower than that setting. If your idle mixture screws (unless it is four corner adjustable) have no variance in vacuum or idle speed, then you ar pulling from your secondaries at idle. You will need to take the cab off and use a feeler gauge at the throtle blades on your secondaries for clearence at idle.

Is this a vacuum secondary or mechanical secondary carburator?

How many CFM is the carburator?

How may cubes is this carurator feeding?

What is your advance at idle?

What is your vacuum at idle?

[Shawn MacAnanny]

Holley 750 4160 vacuum secondary carburetor

converted to center hung float bowls

converted to a 4150 metering block

has Holley adjusta jet primary and secondary metering plates

has an electric choke



I actually fixed the idle this weekend. I loosened up the secondary throttle blades. They were exactly centered it looked like. Now it idles pretty nicely.