[Bobcat]

Patrick .... depending on the cam and idle speed , 7" of vacuum may not be too low . My 482 has a long cam ( 250 @ .050" ) and has about 7" to 8" at 1000 rpm . Having said that , if the vacuum is really that low , then the PV should be in the 3.5 " range ..... and a check for vacuum leaks should definitely be done .
Grubby , you said the timing was ok , but what is your initial and max ? I run 22 degrees initial and 35 degrees max . Ignition/timing should always be checked out before working on the carb .... eliminates one variable . Most carb/ignition people recommend something in the 14 to 18 degree range for initial advance .
550 rpm , for me , is way too low an idle ... I like between 900 to 1000 on my engine .
BTW , as Brent and others have pointed out .... only change one thing at a time or you may have one change cancel out the other . Yes , it`s time consuming , but it`s the best way .