I heard guys say that too,good fuel mileage,good top end,no midrange power.The 2 stage Holley Weber was originally designed for the requirements of a relatively high reving 120 cube 4 cylinder.On a a low reving engine of twice the four cylinder's displacement,there simply isn't enough carb to fuel the needs at peak torque unless you push down the pedal to open the second barrel.That's why two H/W's work well on a typical inline 6,the carbs flow match the engine better.
That being said,your carb could have a lean mixture issue.
