Sounds like a timing issue. Vac advance not working? Put a vac gauge on her and mount on the windshield and see if there is any deviation in vac when it's cold and hot.
Maybe take some pics of how thinks are setup. Would that be some sort of governor installed to control the speed of car?
Also check to see if the throttle opens up completely with the foot pedal.
Engine Test Stand Playlist: https://www.youtube.com/playlist?list=PLwoxyUwptUcdqEb-o2ArqyiUaHW0G_C88 restoring my 1968 Firebird 400 HO convertible (Firedawg) 1965 Pontiac Catalina Safari Wagon 389 TriPower (Catwagon) 1999 JD AWS LX Lawn tractor 17hp (my daily driver) 2006 Sequoia 2017 Murano (wife's car) 202? Electric car 203? 68 Firebird /w electric engine 2007 Bayliner 175 runabout /w 3.0L Mercuiser__________________________________________________________
