I never had any luck running manifold vacuum for the advance. If you start w/ 10-14 deg timing and then add whatever the vac advances it by (my Mallory added 20 deg vac advance until I found out about the adjustment) you end up w/ a ton of advance at idle, 20-30 deg, and a real high idle. My carb could not be closed enough to get the idle anywhere close to 900 w/ all that advance at idle.