Quadrajet Idle Mixture Adjustment - Chevelle Tech
Chevelle Tech join team chevelle as a supporting member  
Chevelle Parts at SS396.com      
GROUND UP & SS396.com         
Official Sponsor of Team Chevelle
     

Auto Insurance

Chevelles.com is the premier Chevrolet Chevelle Forum on the internet. Registered Users do not see the above ads.
Engine AdvertisementGeneral Engine Discussion.

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old Jun 27th, 09, 1:53 PM
496blaze 496blaze is offline
Lifetime Premium Member
Todd
 
Join Date: Dec 2006
Location: San Jose,CA
Posts: 946
Default Quadrajet Idle Mixture Adjustment

Hello,

I am working on my fathers boat which has a 454 with a performer manifold and quadrajet carb. It runs great but when you try to adjust the idle mixture screws you get no reaction at all. I am wondering if it could have the wrong carb base gasket? I have already checked for vacuum leaks btw.

Thanks.
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2  
Old Jun 27th, 09, 2:18 PM
Mike Mike is offline
Lifetime Premium Member
 
Join Date: Apr 2005
Location: North America
Posts: 14,557
Default Re: Quadrajet Idle Mixture Adjustment

Everything you wanted to know about QJ's and more.
See pg 7 ,tech tip 6:
http://www.lbfun.com/warehouse/tech_...ng%20Paper.pdf
Reply With Quote Quick reply to this message
  #3  
Old Jun 27th, 09, 2:25 PM
novaderrik novaderrik is offline
Senior Tech Team
Derrick
 
Join Date: Feb 2002
Location: Howard Lake, MN, USA
Posts: 16,730
Default Re: Quadrajet Idle Mixture Adjustment

if the idle screws have no effect, you need to start out by trying to get the throttle blades closed farther by backing off the idle speed screw. if it won't idle, then put more initial timing in it or hook the vacuum advance to a full manifold source.
__________________
"Detroit hasn't felt any real pride since George Bush went to Japan and vomited on their auto executives, I tell you whut"

-Hank Hill
Reply With Quote Quick reply to this message
  #4  
Old Jun 27th, 09, 5:46 PM
Schurkey Schurkey is offline
Gold Founding Member
 
Join Date: Aug 1998
Location: the Seasonally Frozen Wastelands
Posts: 9,361
Default Re: Quadrajet Idle Mixture Adjustment

Might want to look at this link:

http://cliffshighperformance.com/sim...php?topic=45.0

Cliff Ruggles says that the typical "marine" carb doesn't have the idle air bypass feature. Therefore the throttle blades would have to be opened farther to get an appropriate idle speed. And therefore the idle transfer slots would tend to be uncovered.

Might be a good idea to invest in Ruggles' book:

Amazon.com: How to Rebuild and Modify Rochester Quadrajet Carburetors (S-a Design): Cliff Ruggles: Books Amazon.com: How to Rebuild and Modify Rochester Quadrajet Carburetors (S-a Design): Cliff Ruggles: Books

and see if you can add some idle bypass air to your carb--assuming that everything else is working properly, and you don't have something way out of adjustment, or dirt in the idle air or fuel passages.
Reply With Quote Quick reply to this message
  #5  
Old Jun 27th, 09, 9:25 PM
496blaze 496blaze is offline
Lifetime Premium Member
Todd
 
Join Date: Dec 2006
Location: San Jose,CA
Posts: 946
Default Re: Quadrajet Idle Mixture Adjustment

Thanks for all the great feedback. It does in fact have a marine carb on it so the idle bypass not being drilling could be a possibility. I will not dig in any further since it runs so good.

Thanks again to all.
Reply With Quote Quick reply to this message
  #6  
Old Jun 27th, 09, 11:29 PM
SWHEATON SWHEATON is offline
Team Member
 
Join Date: Jun 2002
Location: N.Y.
Posts: 10,629
Smile Re: Quadrajet Idle Mixture Adjustment

As stated,its very likely a retarded base timing issue causing the idle screw to be set higher then normal to obtain an idle which pushed the prim throttle blades past /out of the idle circut which will make the odle mix screws inactive.

Many marine motor have mild perfcams from factory so try 16-18 deg base timing and i bet the motor well be much happier there.

Adv the base timing will also make you have to decrease the idle enough to drop the prim throttle blades back down into the idle circut so the ildle mix screws will become active again.

If the dist has a vac adv also try hooking it to full intake vacuum all te time too.

Sobefore going nuts digging into the carb take a few mins to try doing the above suggested items which very well may fix the problem.

If not then go deeper into carb issues.

Let us know how you make out .

scott
__________________
SCOTT
1969 CHEVELLE SS396,ORIGINAL #'S MATCH,GOT IN 1978,(In 2001 rblt/bored original 396 .030 to 402)/M20/12BOLT/3:31'S
2006 YAMAHA 1700 ROADSTAR SILVERADO (1 owner ,GOT in 2009,4,700 miles/WK end fun)
1977 KAWASAKI KZ1000 (AM ORIGINAL OWNER ,GOT IN 1977,NOW has 29k miles/WK end fun)
2002 MAXIMA (DAILY DRIVER/1 owner,GOT 3/2013 w-44k miles)
Reply With Quote Quick reply to this message
  #7  
Old Jun 28th, 09, 2:40 AM
496blaze 496blaze is offline
Lifetime Premium Member
Todd
 
Join Date: Dec 2006
Location: San Jose,CA
Posts: 946
Default Re: Quadrajet Idle Mixture Adjustment

Quote:
Originally Posted by SWHEATON View Post
As stated,its very likely a retarded base timing issue causing the idle screw to be set higher then normal to obtain an idle which pushed the prim throttle blades past /out of the idle circut which will make the odle mix screws inactive.

Many marine motor have mild perfcams from factory so try 16-18 deg base timing and i bet the motor well be much happier there.

Adv the base timing will also make you have to decrease the idle enough to drop the prim throttle blades back down into the idle circut so the ildle mix screws will become active again.

If the dist has a vac adv also try hooking it to full intake vacuum all te time too.

Sobefore going nuts digging into the carb take a few mins to try doing the above suggested items which very well may fix the problem.

If not then go deeper into carb issues.

Let us know how you make out .

scott

I don't think I have many options at this point without swapping out the Mercruiser Thunderbolt Ignition. Basically there is no vacuum advance or mechcanical advance to modify. Esentially the distributer is just a trigger that is controlled by a seperate control module. It runs quite well but I would like to be able to adjust the mixture. I will try to lower the idle to see if I can gain some adjustability.
Reply With Quote Quick reply to this message
  #8  
Old Jun 28th, 09, 11:26 AM
SWHEATON SWHEATON is offline
Team Member
 
Join Date: Jun 2002
Location: N.Y.
Posts: 10,629
Smile Re: Quadrajet Idle Mixture Adjustment

Again,try adv base timing 1st before doing anything else because some of the Mercruiser motors have mild perf cams that can use more base timing to see if the motor will tollerate it which i bet it will and if it helps the problem with idle mix screws being inactive.

Scott
__________________
SCOTT
1969 CHEVELLE SS396,ORIGINAL #'S MATCH,GOT IN 1978,(In 2001 rblt/bored original 396 .030 to 402)/M20/12BOLT/3:31'S
2006 YAMAHA 1700 ROADSTAR SILVERADO (1 owner ,GOT in 2009,4,700 miles/WK end fun)
1977 KAWASAKI KZ1000 (AM ORIGINAL OWNER ,GOT IN 1977,NOW has 29k miles/WK end fun)
2002 MAXIMA (DAILY DRIVER/1 owner,GOT 3/2013 w-44k miles)
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply
Chevelle Tech > Mechanical > Engine      Current Topic: Quadrajet Idle Mixture Adjustment
Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.
Email Address:

Log-in

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.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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

Forum Jump


All times are GMT -4. The time now is 7:26 PM.


Is there a site like this for?    El Caminos Camaros Novas Impalas GTO Chevy Punch All Chevys

2009 Team Chevelle - AutoForums