The cure will be with the throttle plates and shafts assuming the linkage back to the secondaries has adequate clearance to keep from holding the secondaries open.
I get a LOT of carbs in here completely rebuild or fully restored with that issue. It's usually the huge secondary throttle plates not correctly centered and indexed so they are fully seating in the bores. Remove the base plate, gently loosen the screws, tap the shaft back and forth to center it and tap the throttle plates into the base plate with a screwdriver handle. Very gently tighten the screws, hold it up to a light and make sure they are fully seated before torquing them on down. Not uncommon to find the shaft twisted slightly and need some "tweaking"......
Too tight on the primary bushings will cause the same issue, or plates not correctly centered, so spend some time there as well.
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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