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Your car has the HIF-6, right? (no separate float bowl, under venturi instead).
Yeah, those drive me crazy sometimes too. The intake manifold up to the piston must be air tight. The HIF-6 used positive seals on the throttle shafts to help with this. If yours are cracked, dry or gone air will leak in and make tuning very difficult.
Spraying starting fluid or WD-40 at suspected leaks should cause the engine speed to momentarily increase or (if really bad) stumble.
Also very important is that they are balanced and working as a unit. Unbalanced (one working more than the other) carbs will never tune properly and can lead to troubles inside the engine. Try slackening the nut holding one of the bell-cranks to the throttle interconnect shaft and adjusting the throttle stop on each carb individually. Getting a uni-syn or similar balancing tool is helpful but you should be able to get it close by holding a small diameter length of tubing to the carb throat (I hold it at the bottom and as close to the piston as possible... exact same position on both carbs) and listening to the tone and volume of the "hiss." Opening or closing the throttle will increase or decrease the "hiss." Once they are more or less identical tighten the bell crank back down. Also ensure there is a little play between the throttle mechanism and the interconnect shaft (pedal moves a little bit before shaft does).
PO may have replaced or tinkered with carbs too. Improper needles can cause nearly as many headaches as worn parts (needle is spring biased and rubs on jet). When you raise the piston (engine off) you should be able to release it and hear the piston tap the top of the jet with a distinct "click" as opposed to a dull "thunk" This results from the jet being centered in the carb body bore. From this "click point" lower each jet the same amount (2-2.5 turns). Adjust richness from there. there may (should) be a little tickler that raises the piston 1/4 inch. Raising a piston and getting a faster idle means too rich. Raising a piston and getting a stumble means too lean. Raising hte piston and getting a momentary faster idle followed by a reduction in revs is "just right."
The bi-metallic lever inside the float bowl is supposed to compensate for increased under-hood temperatures but I don't trust it completely. Turning the mixture adjusting screw moves the lever and that lifts or lowers the jet.
Another source of an over-rich mixture is the choke assembly (technically an enrichment circuit). It can leak causing a pernicious rich condition when improperly assembled or badly worn (o-ring dies).
Ping ranges from a barely noticeable "tick" to a nasty rattle coming from the engine as you apply throttle under load (up a hill). Rattle as you drive up the hill and let off throttle slightly and it goes away is "ping."
Too much info?
Start by trying to balance the suckers then get a decent mixture (jet up or down). Oh, once balanced always make the same exact adjustment to each carb.
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