Hemi carb linkage tuning

Is there a good reference here on Moparts for how to correctly tune a stock dual quad Carter carb set up for the street? Particularly idling and just off idle?

My Hemi runs well, but I do constantly tinker with it. I use a Unisys gage and have both carbs set up so they are contributing equally. I recently read various conflicting posts and stories regarding having the rear carb be the primary, or not. Again, stock linkage. If I did set it up as the rear carb as a primary, how would I know how much is about right?

Before I started using the Unisys to balance the carbs, I was seeing where the front plugs were seemingly a bit leaner than the back, that is what led me to start with the gage.

Thoughts?

I know what I do but I'm going to be quiet and I can hardly wait to read the replies.

I'll wait too but I'll add that any dual quad Chrysler product that I remember had the rear carb as the primary,[or read the shop manual !!

Maybe I am asking this wrong. To quote the manual...”with rear carburetor at wide open throttle, adjust the length of the connector rod so that the front carburetor is also at wide open throttle.” Also concerning idle speed and mixture...”accurate carburetor synchronization or balance is extremely important...”.

So...I have the carbs well balanced using the Unisys tool (Dvorak’s), and throttle linkage set up correctly. I am not running an active choke (Carolina, don’t need).

So how does any of this translate in to rear is “primary”, other than that it is where the linkage connects? How is that defined?

Again, the car runs pretty well, is very streetable, and has been since it was built in 2011, particularly given the rumble it has with the Mopar .524 lift/292 duration cam and the car being an automatic.

I worry that I am missing something. When I had six packs, there were tons of little tricks around setting them up to run well, many well documented here (if I remember the archives have something like a 16 or 64 step plan to running them!). I am not seeing the same for Hemi’s?

The rear carb is the primary carb by virtue of the choke.

And it’s not a coincidence the intake manifold has heat to the back/primary carb plus with the carbs off you will notice that the rear/primary part of the manifold has an interconnection slot cut in it - for driveablity fuel distribution at low speed.

Your going down the correct roads on the adjustments you've made
It ain't a six pack so don't over think two carburetors, which year carbs are you working with?
Are you up for using a wide ban O2 system to put the finest tune on the carbs that you can get? If so shoot for between 14.5 to 15.8 air fuel ratio at idle warmed up and between 13.8 to 15.5 on light throttle cruising below 2500 RPM in high gear and shoot for between 12.2 to 13.8 at WOT in high gear. The numbers I'm recommending are not the absolute best so test your car with your O2 system in your area on your fuel, you and your car may like fatter or leaner than the numbers I found that I liked the best on my last hot street car on Oregon pump swill

I probably am over-thinking it. It’s a 69, carbs too.

I have thought about messing around with A/F ratios, I do have access to a unit. I should give it a whirl. Just got done redoing the distributor on a Sun machine, that was a nice difference, amazing how “off” the distributor was prior (meaning weights hanging up, vacuum can twisting the plate).

Good: No 14 year old experts have replied. You are on the right track, follow the factory instructions they are dead on.
I set the linkage as the factory directs first. Then I screw every mixture needle into bottom (gently) and then screw it out 1.75 turns for a start. In the old days I then started it and tweaked each mixture screw to the smoothest warm idle by ear. Generally they would all end up at the same amount of turns out but unless there was more than 1/2 turn between them all I wouldn't worry about it. A wideband can speed things up these days.

Excellent. Thanks. I do sort of treat it as if setting up a 4 corner idle.

The rear carb is primary because it's the only one that does anything until you floor it.

So you use all 4 idle screws equally? This is what I thought as well, but there are many who say block off front carb/ bottom idle screws and only idle the rear carb. With the ability for better idle fuel distribution at 4 corners vs 2, I wondered what the reasoning for that was...….

Start with all four screws out 2 turns,then start at the front and turn the first screw in until you start to lose rpm's then back out 1/2 turn,do the other front then go to the rear,same thing.If your idle speed changes you will have to do it again until it idles at the correct speed. If it is a original 2x4 barrel application,both front and rear carbs have idle circuits,they are there for a reason,why block them ? This runs like a clock,850 rpm at idle,15 in vacuum,couldn't make it any better !

Yes: All 4 idle circuits must be adjusted. Back carb is the primary because that's the way the manifold was designed. I always found back in the day that the Hemi's and Sixpacks that were having carb problems generally were not adjusted the way the factory recommended them to be.

But that is not a hemi I think you hit it when you said originally the front plugs where lean. You want some contribution on the front carb at idle to prevent lean condition.