Vacuum gauge is your friend, - vacuum leak is constant, fluttering guage indicates fluctuating vacuum, a single, or many out of adjustment valves will cause that, as opposed to a constant leak, like a pcv = steady guage .
jmo
This site had vids of various guage symptoms, they don't load on this pad, hope it does on yours. [URL]http://www.secondchancegarage.com/public/186.cfm[/URL]
I agree with this. Every time I have ever tuned the carb on this engine, even before I did anything to this the vacuum guage has always been low, and bounced 2-4 inches on the guage. It is never steady.