Running a mopar intake with the old DC mechanical 6 pack carbs. Rear half both pass and driver side plugs are very white compared to the front 4 which look normal to slightly dark. A/F meter shows about 14.2 idle- between 12.2 to 13.5 from off idle to medium cruise, hi speed cruise and highway is 13.6 to about 14.3. This is all of the center carb with 64 jets. With all 6 - WOT it's at 13.4. I have upped the jets, but I just think it's odd that the rear 4 plugs are so much leaner looking... any thoughts???

vac leak possibly? The meter is only gonna show the overall AF ratio. I have a "colortune" which would be good for diagnosing that, a special spark plug that lets you see the color of the flame in the cyl as it is running, you want a nice blue like a bunsen burner in a high school chem class, not red and not yellow. EDIT What I would do is drill into the ex manifolds at the offending cyls & take an AF ratio with an LM-1 & you'd cap the mani holes back shut when done. It'd take some doing but I'd wanna know (& get it right if need be).

Rapid has a good point. A vacuum leak in the back half of the manifold (or rear carb) would do that. You could try the old "carb cleaner everywhere that could leak and listen for an idle change" trick too.

If there aren't any leaks, then maybe you need to fatten up the rear carb's fuel mixture? Just a thought.

You need to keep in mind that the stock type Eddy SB six pack intake is a dual plane type intake and you may need to stagger jet the carbs. you have to balance the fuel distribution at part throttle and on the transition circuit when cruising at light part throttle cruise settings. Your AFR reading are right what I shoot for on my cars
Are any of the spark plugs shiny? If so that makes me think intake manifold leak allowing oil to be sucked up into it
You might want to install the next colder heat range spark plugs in those holes if you don't find and fix a intake manifold vacuum leak first
Let us know what you find

I do have one size bigger jets on the deep plenum side, I'll check for leaks, I was very carful to check for any excessive gaps before installing the intake everything looked tight and even without the gasket, I'm using the felpro with the ring around each port. Just odd the way the front 4 have good color, and the rear 4 are white as can be.

You might want to switch the front and rear carbs. to see if the front spark plugs clean up or not I would put new plugs in if you decide to do that test so you get a valid test

Something obviously is leaning the rear cylinders out. After reading and thinking about it,

1. My first thought was a power brake booster leaking but being a dual plane intake its not likely to affect all 4 cylinders.

One could try removing both secondary carbs, blocking them off and run it just off the center to see if the problem improves.
Depending on those results I would proceed to pull the intake, check the sealing on the rear ports and have the intake checked for internal leaks.
Keep us posted

Ok, no power brakes. I've got new plugs in it now but haven't fired it up yet. What I did find that makes some sense now that I think about it ( remember mechanical 6 pack) when I pulled off the outer carbs the transition idle slots were covered, i squared them and when I installed the outer carbs progressive linkage it was pulling the front carb open ever so slightly. Guessing the back carb was not contributing any fuel at idle, and maybe the front was dribbling from the boosters. I'll update when I fire it up and drive it a bit as weather gets better.

What I would do is put the old plugs back in right now (dont start it on the new plugs) & go out on the interstate & pull over & put the new plugs back in and disable the accelerator pump & ease back onto the hiway & go ten miles or so at the speed limit so you are on the main metering system with no corruption from the AP & hopefully not the transition circuit (I ain't a carb guru) & at the right time cut the ign & take you foot off of the gas at the same time & coast to the side of the road & pull some plugs & see what they look like to get a valid read on what the main metering system is doing for AF ratio in the different cylinders. EDIT may need to go 15 miles, todays unleaded gas shows less color.

Reading your latest post would indicate that the front carb was most likely contributing excess fuel to the front cylinders thereby en-richening their mixture. If that in fact is true I would also expect to see have seen some difficultly in setting the mixture screws.

I have been running the mechanical six packs on various motors for about 40 years and will offer the following:

The secondary carbs are just that, secondary.

Think of a 4 barrel with an extra set of secondaries.

The main idle and low speed operation is mainly controlled by the primary carburetor. A very small amount of fuel is contributed by the secondaries during low speed / idle mainly to keep the fuel from going stale in the bowls.

I have always set the the secondaries idle screw about 1/8 to 1/4 turn open on both carbs trying to egt them as equally set as possible. I have then used the center carb for the rest of the low speed /idle operation.

With a bumpier cam and an automatic they can be opened a bit more if needed to get the primary blades in the correct relationship to the idle, off idle transition. Once the secondary adjustment if equalized the linkage should "SLIP" into both carbs with no pressure.
keep us posted

What TJP said sounds right (I missed it), get the carbs straightened out.

The motor is talking to you and you listened
Fix the obvious problems first and go from there
I like clean cold spark plugs, not medium to dark brown from cruising Not hot clean to lightly brown plugs either
I ran my 518 C.I. pump gas low deck six pack stroker motor from 14.8 to 15.3 AFR at idle and light part throttle cruise RPM up to 2300 RPM I was running stock type 440 vacuum carbs modified a lot by C&J Engineering in Whittier, CA, I did take some tinkering on my part to get it where it was absolutely perfect