While you're looking for vacuum leaks,spray around the throttle shaft. The last 3 carbs I've had problems like this with,it was vacuum leaks around worn throttle shafts. Maybe I'm just gun-shy...
Speed


1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck