Number on the carbs??

Edelbrock sells a set calibrated for dual quad setups. I bet you don;t have that.

http://old.edelbrock.com/automotive/mc/carburetors/thunder.shtml

Calibrations are listed verify what you have.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.