1970 chevy 350 bored .60 cam and carb problems

[1972c10]

Ok i have a 1970 chevy 350 bored .60, 10.25: 1 compression, edelbrock 64 cc heads, eps edelbrock intake, 650 edelbrock avs vacuum secondary carb, comp cam thumper duration 279/297 lift 479/465, rebuilt HEI distributor medium advance springs.

I already put in electric vacuum pump for brakes. Still don' have enough vacuum to open secondaries?

Do i need to ditch the 650cfm for a 750cfm mechanical secondaries?
Or is the cam to big?
Or change advance springs in the distributor?
Or something else?

Please help its driving me crazy driving with the 4 barrels barely opening or not at all.

 

[63Half-ton461]

You need to tune the secondary air valve, Edelbrock has taken the guesswork and tuning troubles out of the secondary side of its new carbs by designing an adjustable valve secondary (AVS), which allows you to change the vacuum secondary's opening rate with a quick turn of a screw. Even though the secondary air door is spring loaded, there are no springs to change here. Just loosen one Torqx-head locking screw and turn the adjustment screw to speed up or slow down the secondary's opening rate. It's that easy.