Two Barrel to Four Barrel Upgrade?

I decided to pull the dirty old two barrel off my 1974 318 and replace it with an Edlebrock Model 1405 600cfm 4bbl and a Weiand model 8007 dual plane manifold. I also added dual exhausts using the stock manifolds. The car ran really great with the two barrel. Now whenever I try to floor it, the motor just moans and the car actually slows. Any ideas?

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