rochester 2 barrel m2mc - 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
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 05-24-2012, 10:40 PM
Registered User
 
Join Date: May 2012
Posts: 1
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
rochester 2 barrel m2mc

i have rebuilt a carb on 79 3.8 firebird someone before me has adjust the metering rob screw does anyone know how many turns it should be
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 05-25-2012, 01:58 AM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 595 Times in 545 Posts
Quote:
Originally Posted by mrdjsweet03
i have rebuilt a carb on 79 3.8 firebird someone before me has adjust the metering rob screw does anyone know how many turns it should be
The adjustment you're talking about is called the "adjustable part throttle" setting, or just "APT" for short. Using those terms will help you find additional info on the subject should you want it. The setting procedures will all be for a Quadrajet 4-barrel- but they are basically the same for the Rochester Dualjet 2-barrel you have, which is the primary side of a Q-jet carb, anyway.

The following is with the carb disassembled:

If you don't have the tool that fits the adjuster screw, carefully slot the screw yourself so you can use a small straight blade screwdriver to adjust it.

You may read that 2 to as much as 3-1/2 turns CCW from lightly bottoming the adjustment screw is a starting point. What I always do for a starting point is for the top of the adjustment screw to be just a small amount above the carb body casting w/o a gasket in place. The carb may be richer than needed in that position (or not, depending), but better than than too lean. But in that position the engine can be run safely and further fine tuning can be done, and w/the following modification to the airhorn to allow easy access to the adjustment, it can be quickly and easily adjusted.

After setting the adjuster even w/the body casting, tap out the aluminum plug in the air horn casting using a punch and ball peen hammer, etc.(carefully- support the casting so when you tap out the plug there's no undue pressure put on the casting), then tap the hole for a screw-in plug. That way you can easily adjust the power piston w/the carb on the engine.

From another thread on this:

Quote:
I use the choke or my hand to partially block some of the air into the carb. I set the APT to where there's a slight increase in RPM as I "choke" the carb some, while running @ 2000 RPM. Not so much that it stumbles or tries to stall, just enough to see if- and how- the RPM changes. This indicates I'm just at the lean edge.

Another method (from SMI, IIRC): "simply turn the screw DOWN (CW) 1/2 turn at a time until you experience a "lean surge". (It will feel like someone is moving the throttle, when their not, or a hesitation on light throttle acceleration). Then turn the screw UP, until the lean surge goes away.

If you are experiencing an "off-idle stumble", you can turn the screw up at 1/4-1/2 turn at a time until it is eliminated. But be sure to adjust your idle mixture screws properly first, as they can also cause an off idle stumble.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

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:
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 for yourself.
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.




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
Rochester 2 barrel 2GC Float Settings. JoshuaRhine27 Hotrodding Basics 1 11-02-2011 09:12 PM
rochester single barrel identification unearthly57 Engine 1 10-11-2011 06:52 AM
'76 Rochester 2 barrel problem Geddy Engine 5 08-18-2009 08:25 PM
Rochester 2 barrel questions. impalaman63 Engine 11 06-24-2009 05:09 PM
rochester 4 barrel Rough-Rider Engine 3 04-04-2007 07:05 PM


All times are GMT -6. The time now is 12:46 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.