85 chevy 4.3 liter v6

did it start running ruff after you put the bad fuel in it ? if so it could be a bad fuel filter or you say you have a carb. not fuel injection there are filters in some carbs. where the supply lines hook into .check to see if you have a vacuum leak you can use starter fluid to do this by spraying around the base of the carb. and intake manifold check pugs and wires cap and rotor this is what I would try first if you do this in steps you can eliminate a lot and save money by not buying what you did not really need hope this helps you some gene