4 bbl carb on wrong? - JeepForum.com
 19Likes
Reply
 
LinkBack Thread Tools
post #1 of 51 Old 06-09-2021, 07:27 AM Thread Starter
85Tuxedocj7
Registered User
1985 CJ7 
 
Join Date: Mar 2021
Location: Kinston
Posts: 20
4 bbl carb on wrong?

I think I found why my engine feels weak.

Below are images of my carb and a photo of the same intake I am running.

the Intake appears to have a divided plenum, when my dad and I (I was about 13) put it together, the carb was turned so that the throttle linkage was facing the fire wall and the electric choke was facing the radiator. I pulled the carb off to clean and rebuild it and noticed the intake ports closest to to the engine were sooty while the other two were shiny as new.

the primaries were over the outside ports, while the secondary's were over the engine-side ports... Dad said it felt like the "four barrel would never open."

Would the carb being turned the wrong direction have seriously stunted the power?

notice how my secondary's are dirty while the primaries are shiny?

Attached Thumbnails
My carb.jpg  
Attached Images
   
85Tuxedocj7 is offline  
Sponsored Links
Advertisement
 
post #2 of 51 Old 06-09-2021, 10:43 AM
Hurricane4
Web Wheeler
 
Hurricane4's Avatar
1979 CJ5 
 
Join Date: Jun 2010
Location: Steubenville, Ohio
Posts: 1,538
Garage
What brand/model of carb & intake?

"The unbelievable we can do immediately . . . the impossible just takes a little longer."
My College Accounting Professor

"Success is not final. Failure is not fatal. It is the courage to continue that counts"
Winston Churchill

Jeeps I Have Owned in Year Order:
'61 CJ5, '63 CJ6, '78 CJ5, '79 CJ5 (Current), '79 CJ7 & '86 CJ7.
Hurricane4 is offline  
post #3 of 51 Old 06-09-2021, 07:28 PM
jeepdaddy2000
Registered User
 
jeepdaddy2000's Avatar
1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point
Posts: 9,251
One primary barrel on each side of the plenum.
One secondary barrel on each side of the plenum.

Paperwork will ruin any military force.
Chesty Puller
jeepdaddy2000 is offline  
 
post #4 of 51 Old 06-09-2021, 08:42 PM
BagusJeep
Registered User
 
BagusJeep's Avatar
1981 CJ7 
 
Join Date: Jul 2009
Location: Bali
Posts: 8,385
I am surprised it even ran.

BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
1980 Land Rover Series III 109" troop carrier - ROVER
BagusJeep is offline  
post #5 of 51 Old 06-09-2021, 08:55 PM
JEEPFELLER
Registered User
 
JEEPFELLER's Avatar
1977 CJ5 
 
Join Date: Dec 2015
Location: Western
Posts: 1,301
Garage
I'm a bit lost on the orientation of your carb.

My Holley 390 sits on the 258 with the primaries against the valve cover and the secondary's facing the driver's fender

This being on an Offenhauser intake.

A better description is that it is sitting "Sideways" on the intake for the throttle and such to work out.

Along with this "ODD" configuration is the rearward slant of the engine

This slant messes up the Holley's internal fuel level and the adjustments, as one primary barrel and one secondary barrel is leaning lower on the slanted intake.

Nothing is "EVEN", precise adjustments are almost impossible.

HOWEVER

I had a plastic spacer machined to compensate for the slant---thus making the carb level again

I have a couple of pics of it in the forum

Here's one in this link (crammed with info)

https://www.jeepforum.com/forum/f8/c...258-a-4408347/

In pic 1) notice the air cleaner is "Level" compared to the rear slanting valve cover---thanks to the slanted spacer

Pic 2) compare the valve cover----the spacer is plainly seen in this pic

-----JEEPFELLER
Attached Thumbnails
carb slant12 (2).jpeg   wedge carb nnhy (2).jpg  
Attached Images
 
JEEPFELLER is offline  
post #6 of 51 Old 06-09-2021, 09:04 PM
KevinCJ7Jeep
Registered User
 
KevinCJ7Jeep's Avatar
1981 CJ7 
 
Join Date: May 2017
Location: Wichita
Posts: 328
Is it my bad eyes or is that a spread bore carb and a square bore intake
pedal2themetai likes this.
KevinCJ7Jeep is offline  
post #7 of 51 Old 06-09-2021, 09:40 PM
gutthans
Registered User
 
gutthans's Avatar
1995 YJ Wrangler 
 
Join Date: Jun 2018
Location: Deland
Posts: 1,234
Garage
Depending upon the year of the OFFY manifold, I believe the mounting pad area was changed to a 6* slant to compensate for AMC 258 engine tilt (4*- 6*). (Maybe a number of owners machined the pads themselves? but I believe it was a factory modification. A machined spacer (as noted earlier) will do the same on the earlier models.

The dual plane configuration SHOULD be run with the primaries both facing the valve cover, NOT STRADDLING both plenums. The reason is fairly obvious: The fuel charge will travel different distances at different velocities (and I believe it is correct that each side will run slightly leaner than if they both dump into the same plenum portion). They will both wind up in the chamber, however...and without a dyno you may not/won't notice much difference.

And yes, that does look a bit like a GM spread-bore???
gutthans is offline  
post #8 of 51 Old 06-09-2021, 09:49 PM
KevinCJ7Jeep
Registered User
 
KevinCJ7Jeep's Avatar
1981 CJ7 
 
Join Date: May 2017
Location: Wichita
Posts: 328
Maybe not my eyes then. That would explain why the secondaries aren’t opening. I believe the secondaries are dirty because they could not open and no gas passing thru them and also cleaning them
pedal2themetai likes this.
KevinCJ7Jeep is offline  
post #9 of 51 Old 06-09-2021, 11:49 PM
jeepdaddy2000
Registered User
 
jeepdaddy2000's Avatar
1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point
Posts: 9,251
Quote:
Originally Posted by KevinCJ7Jeep View Post
Is it my bad eyes or is that a spread bore carb and a square bore intake
Square bore.Looks like a Carter AFB
Quote:
The dual plane configuration SHOULD be run with the primaries both facing the valve cover, NOT STRADDLING both plenums.
The barrels ALWAYS straddle the plenum. The plenum separates the planes, which are set up so the runners are as equal in length as possible. Enclosed is a picture of a V8 dual plane manifold. Look closely at the separate planes and the runners they feed. If the carb is orientated so the primaries are both on a single plane, then both barrels will feed only 3 cylinders(6 cyl) or 4 cylinders (V8).
Attached Images
 
mudbfun likes this.

Paperwork will ruin any military force.
Chesty Puller
jeepdaddy2000 is offline  
post #10 of 51 Old 06-10-2021, 03:31 AM
mudbfun
Registered User
1973 CJ5 
 
Join Date: Apr 2021
Posts: 123
Quote:
Originally Posted by gutthans View Post

The dual plane configuration SHOULD be run with the primaries both facing the valve cover, NOT STRADDLING both plenums. The reason is fairly obvious: The fuel charge will travel different distances at different velocities (and I believe it is correct that each side will run slightly leaner than if they both dump into the same plenum portion). They will both wind up in the chamber, however...and without a dyno you may not/won't notice much difference.

That is incorrect. The purpose of a dual plane is to divide the work of each primary/secondary barrel and increase the intake velocity. In other words each plane only feeds 3 cylinders. That provides better low end torque. If both primarys are on the same plane then they will both only be feeding half of the engine!



Even if the intake is a square bore and the carb is a spread bore, it wont matter as long as the manifold is big enough to accommodate the larger secondaries.



PS. Loose the spacer if possible. Dyno tests have proven them to be a negative power accessory.
mudbfun is online now  
post #11 of 51 Old 06-10-2021, 03:41 AM
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 22,331
Quote:
Originally Posted by jeepdaddy2000 View Post
Square bore.Looks like a Carter AFB

The barrels ALWAYS straddle the plenum. The plenum separates the planes, which are set up so the runners are as equal in length as possible. Enclosed is a picture of a V8 dual plane manifold. Look closely at the separate planes and the runners they feed. If the carb is orientated so the primaries are both on a single plane, then both barrels will feed only 3 cylinders(6 cyl) or 4 cylinders (V8).
That would be true with an ordinary split plenum setup where one plenum feeds 1/2 the cylinders evenly but the Offey split PLANE manifold is a little different.

[off topic]Actually you want the cylinders to draw air evenly, You do not want 3 cylinders in a row drawing air/fuel and then nothing for a revolution while the other plenum isn't supplying any mixture for a while and then suddenly needs to supply a lot. It cuts the momentum of the air flowing through the carb messing up the mixture. Equal runner manifolds are a little different design than the one pictured. [/off topic]





The plenum is split where each plenum is feeding all the cylinders. the narrower passages are for the primaries to keep the flow moving fast for better throttle response while the large ones are for the secondaries where large amounts of flow are needed.

So you would want you primaries on the smaller side and secondaries on the larger side.


Quote:
Originally Posted by gutthans View Post
Depending upon the year of the OFFY manifold, I believe the mounting pad area was changed to a 6* slant to compensate for AMC 258 engine tilt (4*- 6*). (Maybe a number of owners machined the pads themselves? but I believe it was a factory modification. A machined spacer (as noted earlier) will do the same on the earlier models.

The dual plane configuration SHOULD be run with the primaries both facing the valve cover, NOT STRADDLING both plenums. The reason is fairly obvious: The fuel charge will travel different distances at different velocities (and I believe it is correct that each side will run slightly leaner than if they both dump into the same plenum portion). They will both wind up in the chamber, however...and without a dyno you may not/won't notice much difference.

And yes, that does look a bit like a GM spread-bore???
Looking at the pictures above. Looks like one manifold has the narrow passages on top and one manifold has the narrow passages on the bottom.
This would have a BIG effect on how the carburetor is mounted.

If you mixed up the primary and secondaries then you would have probably the same performance as a too tiny 2 barrel and when the secondaries opened up, they would have to squeeze through those narrow passages, ot doing much to increase performance.

If that is a spread bore carb then the secondaries would never open all the way.

The top one pictured above is for 81 and later as it has no provisions for heating the manifold and the thinner mounting pads.
The bottom one is for earlier 258's as it has a flange on the bottom so the exhaust manifold can attach to it so the exhaust can heat the bottom of the manifold and the mounting tabs are longer to bolt up to the stock exhaust manifold.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


I drive a Prius to save money and buy more Jeep Parts....
John Strenk is offline  
post #12 of 51 Old 06-10-2021, 04:20 AM
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 22,331
Quote:
Originally Posted by mudbfun View Post
....

PS. Loose the spacer if possible. Dyno tests have proven them to be a negative power accessory.
I think that depends upon the manifold design.

On some manifolds it helps with smoothing the airflow out the carb giving it a chance to mix properly.

If the base of the carb is mounted on a manifold that instantly changes direction to the left and next instant to the right, you going to get different mixtures in either direction.

Smooth air flow out is just as important as smooth air flow in for "drivability"

If you only run at WOT then that changes everything also as opposed to driving to the grocery store during the week.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


I drive a Prius to save money and buy more Jeep Parts....
John Strenk is offline  
post #13 of 51 Old 06-10-2021, 05:30 AM
jeepdaddy2000
Registered User
 
jeepdaddy2000's Avatar
1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point
Posts: 9,251
Quote:
Originally Posted by John Strenk View Post
That would be true with an ordinary split plenum setup where one plenum feeds 1/2 the cylinders evenly but the Offey split PLANE manifold is a little different.
I stand corrected and owe gutthans an apology.
My depth of knowledge of 4 and 6 barrel intakes is showing.
Axhammer likes this.

Paperwork will ruin any military force.
Chesty Puller
jeepdaddy2000 is offline  
post #14 of 51 Old 06-10-2021, 07:26 AM
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 22,331
Quote:
Originally Posted by jeepdaddy2000 View Post
I stand corrected and owe gutthans an apology.
My depth of knowledge of 4 and 6 barrel intakes is showing.
Not a problem.

You should of seen the intake manifold on my Renault driven Lotus Europa.
One barrel of the single 45DCOE fed cylinders 2 and 3 while the other barrel fed cylinders 1 and 4.
SCCA did say you could run any 2bbl carb and still remain in stock classes.
KevinCJ7Jeep likes this.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


I drive a Prius to save money and buy more Jeep Parts....
John Strenk is offline  
post #15 of 51 Old 06-10-2021, 08:44 AM
Fourtrail
Registered User
1974 CJ6 
 
Join Date: Dec 2007
Location: Illinois
Posts: 5,234
Quote:
Originally Posted by John Strenk View Post





The plenum is split where each plenum is feeding all the cylinders. the narrower passages are for the primaries to keep the flow moving fast for better throttle response while the large ones are for the secondaries where large amounts of flow are needed.

So you would want you primaries on the smaller side and secondaries on the larger side.



Wherein lies part of the issue, the Edelbrock carb does have mechanical opening secondaries, but there is a weighted air valve between the venturi and the butterflies in the base plate. If you are not creating enough vacuum on the secondary side of the intake, the air valve will not open and no fuel will flow through. With the larger runners on the secondary side of the offenhauser intake, it is possible that you just aren't getting enough vacuum signal to open the secondary air valve. One option is to drill a small hole in each weight to reduce the mass so the secondary air valve will open/open quicker. Just don't go too much, then you are ordering a new secondary air valve if it opens too quick and causes the motor to stumble.


Image is of the air valve that sits between the venturies and the butterflies.
Attached Images
 

80 CJ-5, 74 CJ-6, 56 CJ-5
Fourtrail is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



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 Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome