Dual quad set-up. Kinda long.

[Crazy440]

Was at my local auto parts store, having coffee with the owner.  A guy comes in, to get some oil, for his rig.  Jeff (the owner) introduces us.  The guy (Paul) asked me if I was the owner of the nasty Mopar, running around?  He mentioned that he has a 58 Impala with a dual quad 348, 4 speed.

I asked if it would be possible the see it and I followed him to his place.  Very nice plain Jane blue and white rig. Sounded really healthy.  He followed me to my place, to check mine out.  While talking with him, he asked how I had my carbs set-up.  Note:  We both have Edelbrock intakes and the same carbs.

Here's where it got interesting.  He mentioned that a lot of factory dual quads, did not come with idle circuits, in the front carbs.  You start by backing all the way out, on both of the throttle linkage idle screws.  Then turn them each, 1/2 half turn,at a time, until it will start and stay running.  You then adjust each the same amount of turns, until you reach your target idle rpm.  Next you seat the front idle adjustment needles, close the front throttle and make all vacuum hook ups, to the back carb. PCV, brake booster, etc. No progressive linkage. Then you hook a vacuum gauge, to the back carb and set the idle mixture and you are done.

He says he has used this method on 4 different rigs. 3 Chevy.  1 Ford.  The Impala has been running this way for 5 years.

After he left, I sat in the garage and thought about it and it actually made sense.

What's every ones thoughts, on this?
Thanks

[Crazy440]

Anyone?

[1974dodgecharger]

whatever makes it run better 

getting all technical is for folks who are trying to get max HP out of their cars.


Install a wideband in the car and play around with the carb adjustments you will see some interesting things.  Installing a wideband helped me understand whats happening why I did this and why that happened. 

[XH29N0G]

Seems to me that closing down the idle adjustment screws on the front carburetor and opening them up on the back one, but still having the butterflies open enough by the same amount on both to allow the car to idle would make both carburetors admit the same amount of air, but the back one contribute more gas, making the front more lean than the back (at idle).

I do not know how this would translate to cruise RPM and assume there would be little effect at WOT.   The question is whether it matters for engine health or performance.  If it was done for cars supplied from the factory, my guess is that it is OK for engine health and didn't make a big difference for performance.

Keep in mind that I am not a mechanic or carburetor person, so someone else may have a better idea.