383 dual quads lean at idle and cruise

It has a divider straight down the manifold dividing the 2 banks. It’s not a true dual plane. The carb adapters are also divided.

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I’m not a fan of the 360* Offy manifolds in general.

I’d try a couple of open carb spacers so the two sides can both pull off all the carb circuits.

And when you get tired of messing with that, put an RPM on it.