how much vacuum for secondary's
I have a stage 2 q-jet from jet performance, i recently put new heads and a cam in. The cam is kinda big, 107 lobe separation adv dur 287/297 about (thumper comp cam). edelbrock performer rpm heads. Its all on a chevy 350 w/ a performer intake. Im looking to get a different carb seems to be running lean and im not sure if the vacuum secondary's are opening. The engine pulls about 10-12 manifold vacuum. how much is required before your forced to have mechanical secondary's? im looking into a holley or a demon carb. any recommendations or ideas?