Gas that contains ethanol (corn alcohol) gels clogs into clumps of yuck garbage ~ I don't think these older classic vehicles were designed to run on crap gas ~ since I began using non-ethanol gasoline my truck runs twice as nice as before so much better smooth idle better acceleration too ~ if you want even more performance visually inspect the catalytic converters for blockage & check brake drag & clean regrease adjust the front wheel bearings & replace all fluids engine oil transfer case transmission differential lubes & replace all filters especially the air filters ~ PCV if not clean and functioning properly will also cause a rough idle ~ don't forget the wiper blades ;p

Test the air casing snorkle hot air valve used for faster engine warm up -- any vacuum leak in it's diaphragm will cause it to remain open forcing hot air into the engine -- cap off the vacuum connection under the carb which defaults this valve to stay in the closed position which causes the air intake to ingest outside colder air -- sneaky thing !!