Quadrajet Idle Strangeness - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- 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 07-16-2007, 08:12 AM
Registered User
Last photo:
Join Date: Feb 2006
Location: Chattanooga, TN
Posts: 114
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Quadrajet Idle Strangeness

I've installed a rebuilt quadrajet and a Performer intake on my pretty much stock 305 daily driver. The rebuild of the carb was very detailed, even removing and cleaning out the idle tubes and blowing out all passages. The throttle shafts have bronze inserts already installed and I've checked and re-checked the float level, but I still have a strange idle condition.

When the car is warmed up it will idle at a consistant rpm then drop and idle much slower for 5 seconds or so, after which it goes back to the faster idle which it will maintain for about 10 seconds before dropping down for another 5 seconds, etc. etc.

I've attempted to look into the carb while it does this, but I've seen no evidence that the main jets are expressing gas when this happens. This carb has the adjustable part throttle, but adjustments to it have had no effect on this condition, nor has any of the adjustemnts to the idle screws. I now drive the car idled higher than I'd like just to keep it from stalling when it does decided to drop down to it's lower idle speed. I've though maybe the fual bowl is being overfilled by a faulty needle seat or something. But it doesn't figure that it would overcome that within 5 seconds of only idle consumption.

Any ideas? I'm a quadrajet fan and I've owned some great ones, but this has me miffed. I've been trying everything I can think of and nothing seems to help.

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 07-16-2007, 08:37 AM
302 Z28's Avatar  
Last photo:
Join Date: May 2003
Location: North Texas
Posts: 10,940
Wiki Edits: 0

Thanks: 1
Thanked 120 Times in 101 Posts
Assuming the idle passages are all free of obstructions, I would suspect a vacuum leak or fuel puddling on top of the butterflies. Do you have good adjustability with your idle adjustment screws?

Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-16-2007, 03:52 PM
DHMag's Avatar
Registered User
Last photo:
Join Date: Jun 2005
Location: InCahoots, Texas
Posts: 302
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
im thinking its something outside the carb. EGR, PCV...
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-16-2007, 04:15 PM
DoubleVision's Avatar
Not Considered a Senior Member
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 43
Posts: 10,733
Wiki Edits: 0

Thanks: 19
Thanked 77 Times in 71 Posts
If the idle screws have no effect there has to be another reason for it just as Vince said. A vaccum leak or fuel puddling. Years ago I had one that had to much fuel pressure, and it was flooding out of the idle passages so you couldn`t see it, and it was very difficult to figure out, but what gave it away was, after I would shut the car off it would continue to smoke out of the carb for about the next 10 minutes, that white hazy looking mist would rise out of the carb for a long period, that`s what told me something was amiss.
What is the fuel pressure? have you made any changes to the fuel system? is the vapour line still open that goes to the fuel tank? is the carbon canister still in use?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-16-2007, 05:58 PM
F&J F&J is offline
Registered User

Last journal entry: 32 Ford cabriolet conversion/windshield
Last photo:
Join Date: Mar 2007
Location: Connecticut
Age: 65
Posts: 1,571
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
things on quadrajets I've seen:

-leaking welch plugs on the bottom of the main body casting. These are notorious for leaking, and most rebuilders put a special sealer over the plugs when the base is off. This also causes the bowls to be empty in a day or so, if you don't drive it much.

-Internal vacuum leak caused by warping. This usually makes the car almost seem like it's got a slight "cam", by the way it idles, and adjusting the mixture does still afffect idle quality, but can't seem to get it stable. Just went through this with a late 70s vette. It had a new kit and new gaskets did not help.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-16-2007, 07:36 PM
Registered User
Join Date: Jun 2007
Location: west. Colo
Age: 60
Posts: 26
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I agree the plugs can and do leak. they need to be checked and or epoxied
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
Too much camshaft!? pi71 Engine 22 04-10-2007 01:18 PM
Cam lope question joeford Engine 4 08-10-2006 08:14 AM
Quadrajet Idle Adjustment tool ? ? Theresa Shank Engine 8 05-30-2006 10:36 AM
I'm going to make a bonfire out of my car blown69stang Engine 36 08-22-2005 03:36 PM
Quadrajet Idle question Ryan Martinez Engine 6 05-20-2005 04:12 PM

All times are GMT -6. The time now is 09:08 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 Hotrodders.com 1999 - 2012. All Rights Reserved.