Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Adjusting Q-Jet for SB350 - running rich

Discussion in 'The Garage' started by Jim Johnson, Feb 16, 2004.

  1. Jim Johnson

    Jim Johnson Registered Member

    Joined:
    Jan 26, 2003
    Posts:
    64
    Likes Received:
    0
    Location:
    Middle, TN
    I am pretty sure my truck is running rich - I keep fowling plugs ( they are always dark and moist looking) and I also have some sluggish repsonse in lower to mid range RPM's - especially when it is cold

    I know there are 2 adjustments on the front, one is the idle, and I assume the other is the air/fuel mixture?.....seems like I heard there was a 3rd adjustment on these.... ( I have a Q-jet for about a 72 chevy - no emission controls)re-build carb, bought from Autozone about 1 year ago....
     
  2. shane74

    shane74 1/2 ton status

    Joined:
    Feb 12, 2002
    Posts:
    4,100
    Likes Received:
    0
    Location:
    Vancouver, WA
    You should have two screws on the front of the carb for adjusting fuel and air. What I do, with the truck running, is turn them all the way in (it'll start running real crappy) and then back them out about 1 1/2 turns (or until it starts to idle good) and work my way from there. Also, have you checked your timing? That could be a big part of it to.
     
  3. pauly383

    pauly383 Daddy383 Staff Member Moderator

    Joined:
    Jul 22, 2001
    Posts:
    16,217
    Likes Received:
    1
    Location:
    Mesa , Arizona USA
    There is a third adjustment but it is internal and a P.I.T.A to do cause you must remove airhorn. Some of the good rebuilds have a hex plug over this and change it to adjust easily from the outside. It adjusts how far the rods can travel up and down . By all means DON'T adjust it if you are unsure /forums/images/graemlins/k5.gif
     
  4. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

    Joined:
    Apr 5, 2003
    Posts:
    999
    Likes Received:
    593
    Location:
    Pueblo, CO
    The two screws on the front of the baseplate are just the idle mixture screws. Adjusting these will not effect the part throttle/full throttle mixture. That is done by the meetering rods for the primary and secondary side (two pair). If its just the part throttle/cruise mode that is running rich you should be able to work with running a larger rod on the primary side.

    The problem is, Q-jet rods/jets/hangers are not easy to come by only Edelbrock has any of that stuff now and it's pricy. You might be better off to run down to the local boneyard and pull the lid's off of all the q-jets in the yard (if they still have the engines) and take the rods, jets and hangers. I did this a few years back and put together a good selection. Then go get the Rochester Quadrajet book published by HP Books. that book has an excellent guide to setting up a Qjet by jet size, rod size and hanger length.

    That being said don't overlook the basics. The float level may be set to high, causing the rich condition. Another issue common to Qjets is too much idle speed adjustment exposing the transfer slot pulling fuel from it in addition to the idle circuit. One more issue leading to a rich condition could be from the plugs in the bottom of the main body of the carb. These plugs are just there to fill a hole from the casting process, but are known to leak over time. This leak is just above the throttle baseplate and gets pulled right in with the rest of the fuel from the carb. The fix is to remove the baseplate and mix up some JB weld, clean the plugs and surrounding area on the carb and apply the JB weld to the plugs to seal them up. If those issues are not there, then start looking at the meetering rods.
     
  5. shane74

    shane74 1/2 ton status

    Joined:
    Feb 12, 2002
    Posts:
    4,100
    Likes Received:
    0
    Location:
    Vancouver, WA
    Thanks for the education! That's why I like this site so much! /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif I learned something new today! /forums/images/graemlins/cool.gif
     
  6. crawlink5

    crawlink5 1/2 ton status

    Joined:
    Oct 9, 2003
    Posts:
    431
    Likes Received:
    0
    Location:
    Spring, TX
  7. crawlink5

    crawlink5 1/2 ton status

    Joined:
    Oct 9, 2003
    Posts:
    431
    Likes Received:
    0
    Location:
    Spring, TX
    Good detailed info on Q-jets

    http://www.73-87.com/7387garage/garage_drivetrain.htm

    http://hotrodders.com/kb/engine/articles.html#carburetor

    http://www.carcraft.com/howto/57178/

    Quote from an article:
    "A good book that everyone who has a Q-jet should have is Doug Roe's Rochester Carburetors. This is The Bible for Rochester carbs, hands down. I can't stress this enough, if you want more performance out of your Q-jet or just want a great how to rebuild reference, buy this book. It is an invaluable piece of information that you shouldn't pass up."
     
  8. lukebaby1

    lukebaby1 1/2 ton status

    Joined:
    Dec 16, 2003
    Posts:
    231
    Likes Received:
    0
    Location:
    Richmond, Virginia
    Thanks for the links! /forums/images/graemlins/peace.gif
     

Share This Page