Kavesh,
Heres a test drive on youtube

http://www.youtube.com/watch?v=cxQZUYcqm4A

I made a movie to show the carb runs good.
But, at about 1:56 you can see the gages with it in Drive.
The vacuum gage is 2nd from the right and marked 0-10-20-30 inches tho you cant read the numbers. But, you can see it runs 18-19 inches of vacuum in drive. This is a stock cam 292 but the stock cam 250 is similar. The cams in these are very mild so they have a lot of idle vacuum.

If your idle vacuum is low but steady and its not a vacuum leak, I'd suspect either
* VERY wrong timing, way retarded, damper messed up maybe?
* Carb idle circuits badly clogged. Try closing the choke plate almost all the way while its idling warm. If it speeds way up as its almost closed, then you either have a vac leak or dirty idle circuits.
* Cam gear is a tooth off, tho thats unlikely.