Quadrajet Question

[demian5]

Hi -

Im pretty familiar with rebuilding Q-Jets, but I have ran into a couple that have me stumped. I have rebuilt two in a row and both act like they have a vacuum leak afterwards. The mixture screws do nothing. Pulled them, apart, everything looks great! No clogged passages. And of course the shaft bushings leak a tiny bit but not the amount that im expereincing.

Timing is set to 10 BTDC. No Vacuum leaks on the truck verified by disconnecting all vacuum coming off the intake and carb and plugging off (including booster). Intake manifold gaskets are recent and not leaking.

AND I put on a brand new demon carb, and no problems. But both of these Q-Jets, same thing.

Anyone run into this? Maybe I missed something inside?