carb headache
Thread Starter
Instructor
Joined: Sep 2010
Posts: 216
Likes: 0
From: Seymour Indiana
carb headache
I ended up putting a Holley street avenger on my 77 today, I got everything swapped and runnin but I'm about to pull my hair out. The idle wont come down from 2500. It runs smooth and is very snappy with no dead spots. I checked and cant find any vacuum leaks. So I was wondering if anyone on here that has put a holley on their vette can answer a few questions. These cars seem to have a few more vacuum lines and was wanting to check if I had some in the wrong place. I still have the egr valve hooked up, the brake booster, vacuum advance on distributor, and the vacuum line that, if I'm not mistakin, goes to vacuum canister for head lights all plumbed into it. 
I don't know where to look. Never had this problem before and I spent hours trying different things. If anyone has any words of helpful wisdom I would greatly appreciate it.
I don't know where to look. Never had this problem before and I spent hours trying different things. If anyone has any words of helpful wisdom I would greatly appreciate it.
Race Director
Joined: Apr 2000
Posts: 17,672
Likes: 199
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Did you touch the distributor ?
You obviously know there is an idle set screw on the carb ?
You can disconnect and plug most vacuum lines going to and from the carb while stationary to see if it vacuum problem.
Always use a new carb to manifold gasket when changing carbs as the previous carb will ususally have made indentations in the existing gasket that will not match up with the bottom plate of the new carb resulting in a vacuum leak.
Normally a vacuum leak will not raise the RPM's that much
This goes on all my posts: Please report back to those who helped you the final outcome of your initial post
You obviously know there is an idle set screw on the carb ?
You can disconnect and plug most vacuum lines going to and from the carb while stationary to see if it vacuum problem.
Always use a new carb to manifold gasket when changing carbs as the previous carb will ususally have made indentations in the existing gasket that will not match up with the bottom plate of the new carb resulting in a vacuum leak.
Normally a vacuum leak will not raise the RPM's that much
This goes on all my posts: Please report back to those who helped you the final outcome of your initial post
Last edited by MotorHead; Mar 15, 2011 at 08:39 PM.
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
I have had 2 avengers do the same thing. Basically too much air and drawing fuel. Both were the secondary throttle plates not closing completely at idle. Look with a flashlight and see if they are, or you might have to pull the carb to see. I needed to remove the secondary plates and sand them smooth with emery cloth to get a good fit.
Thread Starter
Instructor
Joined: Sep 2010
Posts: 216
Likes: 0
From: Seymour Indiana
Yes I pretty much unscrewed the idle screw all the way out with no change. I didn't touch the distributor. I adjusted the idle mixture screws with no change and everything is new, new gaskets (had to use a carb spacer so Holley would bolt to intake) new carb, new vacuum lines.
Racer
Joined: Jan 2008
Posts: 291
Likes: 15
From: Virginia Beach VA
I'm assuming you already checked this, but since I just installed a Holley Avenger myself on Saturday and had the same problem I thought I would share anyways. I adjusted my throttle cable bracket too tight. In "taking out the slack" in the cable I got a little over zealous and it wouldn't return all the way to idle. Figured out the problem by disconnecting the throttle cable with the engine running. I felt like a big dummy. Good Luck 
Thread Starter
Instructor
Joined: Sep 2010
Posts: 216
Likes: 0
From: Seymour Indiana
Well I just went and checked a few things and I noticed the choke wasn't opening. I pushed it open and a few seconds later the rpms dropped a little but not much, still over 2000, I'm wondering if the fast idle speed screw is set too high.
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
If the choke is the issue, let it warm up enough to run and on the passenger side of the carb behind the electric choke body is a red or some color fast idle cam. Push down on it with your finder to get it off fast idle and that will tell you if that is your issue. Also like the other post said, diconnect the throttle cable and see if it is pulling on the throttle. Now see if the idle speed drops or is adjustable to what you want. If you have the throttle cable off and the auto choke off and the idle speed set screw adjusted, and no major vacuum leak and it still idles way too fast, then there is something hanging up the throttle plates, bind, alignment, gasket material from the spacer or ??.
Last edited by bigvette1; Mar 16, 2011 at 06:01 AM.
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Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
did you check the little set screw on the secondary plates. I put a street avenger on my 68 mustang and had the same problem. Turned out that from the factory the set screw that sets the resting spot for the back blades was open too much. Once I adjusted it back down to the correct distance the idle was right.
Thread Starter
Instructor
Joined: Sep 2010
Posts: 216
Likes: 0
From: Seymour Indiana
Thanks for all the help guys. Got it straightened out and boy does it run strong now. That's one mean little Carb. Turned out to be the fast idle screw was set too high and the cam lever on the choke was hanging up on the bracket the fast idle screw was in so I filed the steps down a hair on the cam so now it idles at 900 smoothly.
