Vacume Problem?

So lemme get this straight. With you vacuum advance hooked up to ported source, you have a stumble at light throttle. You should be able to "step through" the flat spot and the engine pulls fine from 1/4 throttle to full throttle. You remove the hose from the dist and cap it. The stumble goes away.

If this describes you problem, the vacuum advance unit probably has a leak and needs to be replaced. Verify with a mitghty-vac or similar hand pump.

If this does not describe your problem, it's not your problem. Check PVC valve, accel pump shot etc.

What is your carb/cam/intake combo? What is your vacuum at idle? What is your timing?