What are you working on/with? Engine and distributor information would help.
You have dual carbs, I'm assuming a moderate to aggressive cam, you'll want to start timing at 14-18 base and have a total of 36-38 mechanical degrees, maybe more depending on compression. You can usually use another 10-12 degrees of vacuum advance on top of that, as long as it too is dialed in correctly.
I've been known to drill and tap 1/8" pipe thread holes in manifolds to get vacuum. You may have to do the same.
Devin
