What list # are your carbs? I'll look them up in my Holley master parts catalog and give you he stock jetting for the center carb and the part number for the outboard mixture plates and hole stock hole sizes, hopefully.
Me thinks someone may have mess with them before you got them work
On the power valve the vacuum rating shouldn't have any affect on the idle unless you have the idle speed screw adjusted up far enough to make the center carb idle on the transition circuit, you can check that by removing the center carb and flip it over after draining the gas out of it and see how far the throttle blades are opened in relation to the rectangular slot in the front center of the carb throttle plate scope if you can see any of the slot below the throttle plates it is to far open and idling on the transition circuit tsk
I check the power valves by removing them and then use my mouth and tongue to suck on them and make my tongue seal against the center hole, if the valve stays closed with my tongue on it is good, if it doesn't stay closed it is bad scope A ruptured power valve will make it idle rich all the time due to leaking fuel into the carb.
I use a vacuum gauge to check the idle vacuum and install a power valve that is one to two inches lower in vacuum, if it idles above 8.0 inches I use the 6.5 rated valves thumbs If it idles at 5.0 inches in gear like my old pump gas stroker motor did I would use either a 3.5 or 2.5 thumbs
I used both in it and it work the same, not so on the 4.5 tsk
Do you have a pin vise and a good small (.011 to .060) set of drill bits? If so use the drill bits to see what size the bleed holes are on your carbs, the center ones are the idle bleeds and outboard ones are the high speed bleeds scope Post them on here and I'll look up which size they where stock , if I can find them in my catalog luck
I've owned, tuned and driven a bunch of stock 340 and 440 six pack cars with the stock carbs, they would idle great and drive okay with the stock jetting and so on. You can make those motors run a lot better by proper jetting and tuning wrench up
Open the outboards idle mixture screws to 1/2 turn and the center to 2 full turns out from bottom and then use the center carb mixture screws to get it to run as lean as you can when warmed up and set the speed idle at or below 1000 RPM so the center throttle plates are not opening up to the transition circuits wrench scope
It is snowing here, hopefully it will not snow after tomorrow, we need the water but it is mid March work
Good luck on this, you can fix it thumbs

Last edited by Cab_Burge; 03/15/20 02:10 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)