The Answer 99% for Sure - somebody else already mentioned it here already. Since the six pack setup worked fine on the 383 and now it opens so quickly the engine bogs on the 440.....the vacuum hoses are hooked up wrong. Look at your 3-way-Tee vacuum hose that connects all 3 carburetors. The hose for the middle carburetor should be connected to a nipple on the body of the center carburetor. I bet you $2 you've got that vacuum line connected to the nipple on the baseplate of the center carburetor....where the choke pulloff should be connected. THAT port at the base of the center carburetor has full manifold vacuum. Your outboard carburerors are being pulled open constantly and you're only noticing it when you floor the pedal. Check those hoses vs. a picture in a factory service manufal. Nipple on the side of the center carb goes to the 3-way vacuum tee. Nipple on the metering body goes to the distributor vacuum advance. Nipple on the baseplate goes the the choke pulloff. They're all the same size hose/nipples so easy to mix up.