Can't Set Idle - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 10-29-2009, 11:16 AM
10mikeymike's Avatar
Registered User
Last photo:
Join Date: Jul 2008
Location: Northville, MI
Age: 71
Posts: 51
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Can't Set Idle

I just got my 355 SBC back together and can't set the idle. The engine has and Edelbrock 2 X 4 RPM Air Gap manifold with 2-500 cfm Thunder Series AVS carb's. It has a Comp 280H grind cam with an MSD 8570 small cap distributor, 6A box and no vacuum advance. It fired right up on first start and still does, but wants to idle at 2000 RPM. If I back the timing off to 0 degrees initial advance it will idle down to 800-900 RPM, but the headers soon begin to glow. If I bump it up to 10 degrees, it runs right up 2000 RPM. There are no vacuum leaks at the carb or on the manifold. The linkage is properly adjusted and there are no kinks in the throttle cable. The idle speed screws are backed out and off of the cams. The idle mixture screws on both carbs are out about 1 turn. It has an electric choke on the primary carb and the butterfly is closed on cold starts. The butterfly on the secondary carb is fixed in the wide open position per Edelbrock's instructions. It appears neither carb has a fast idle cam or means of fast idle adjustment like their Performer carbs. I called Edelbrock tech support from work and all they reccomended was 16 degrees initial advance, but I'm afraid that much advance will have it idling at 3000 RPM.

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 10-29-2009, 01:08 PM
lg1969's Avatar
Google "Tunnel Ram 406"
Last photo:
Join Date: Oct 2007
Location: Bohemia, L.I.N.Y.
Age: 67
Posts: 1,088
Wiki Edits: 0

Thanks: 2
Thanked 26 Times in 23 Posts
Either you have a stuck throttle shaft that could cause the blades to stay open or a real bad vacuum leak. Is the vacuum port for the PVC connected?
For a motor to run 2000RPM that is a lot of air getting sucked in somewhere else.

Last edited by lg1969; 10-29-2009 at 01:15 PM.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 10-29-2009, 02:32 PM
66GMC's Avatar
Get in, sit down, hang on

Last journal entry: Cab Removal
Last photo:
Join Date: May 2005
Location: Olds, Alberta Canada
Age: 59
Posts: 2,764
Wiki Edits: 0

Thanks: 33
Thanked 94 Times in 89 Posts
Originally Posted by 10mikeymike
The butterfly on the secondary carb is fixed in the wide open position per Edelbrock's instructions.

I was going to suggest that you look under the base of both carbs to make sure that the secondary butterflies were in the 100% CLOSED position. Holleys, for sure, do have an adjustment screw for the secondary throttle plates that is only visible /accessible from underneath.

Are these carbs new or used?

Sometimes it is neccesary to drill a small hole in the primary butterflies in order to address mixture screw problems. (Mixture adjustments are completely ineffective when the throttle blades are above the transfer slots.) If these are used carbs that have had this done, and your engine doesn't have this requirement ... that would cause a "too fast" idle.

Thinking more about the fact that the Edelbrock carbs are of the "AVS" (Air Valve Secondary) design ... maybe the WOT thing makes a bit more sense.
Perhaps an adjustment to the tension on that AVS spring is all you need. Perhaps it's set too weak, allowing it to open at too low an RPM.

Somethings obviously letting too much air in if the primary speed screws are both completely off their seats, and it's still over-speed.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Carbureted Vortec giving rough idle, dieseling after cutoff TNshadetree Engine 17 04-17-2014 09:36 AM
acceleration flat spot in carb. corvettetonybone Engine 17 04-13-2013 08:31 PM
how to boost reference an edelbrock Kilrcady Engine 5 04-26-2009 11:28 AM
DARK brown--BLACK plugs SBC Joshua Lee Engine 128 02-03-2008 09:12 AM
vacuum advance help batman09 Engine 14 09-09-2004 09:42 PM

All times are GMT -6. The time now is 12:16 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.