[Gaz64]

That certainly is a problem in how the secondary barrels operate.

I don't know how long since the last carb rebuild.

I would suggest feeling what each secondary shaft feels like as you open each set of butterflies from closed to open.

Wedge the primaries to wide open throttle once, and check the secondary barrels.

If you have a binding shaft or both, then the carb bases may be warping slightly.

I absolutely hate any thick gasket without any crush limiting spacers.

If the secondary vac chambers don't have the check ball, that's part of the problem.

Can we see what springs are fitted?