[Jack21]

The "hunting" sounds more like distributor than carb. You've checked the vacuum advance which is where I would have looked first. Next, check the mechanical advance. Is the timing moving when this idle speed changes? Disconnect vacuum line from carb to dist, plug carb port, and check with timing light. If timing moves as idle RPM changes, distributor is causing this. First place to look is advance weight retention and advance springs.

If dist is OK, look for something changing your A/F ratio. Crack in power brake line, worn, or wrong PCV valve would be my next suspects.

One thing I always do to insure a good vacuum seal between carb and intake is apply some wheel bearing grease to both sides of the carb to manifold gasket.