a gasket or manifold leak would make the intake charge too lean and would effect multiple cylinders.
typical means of testing is to spray starter fluid or WD-40 or something around the base of the carb and where the intake attaches to the heads. if the engine rpm speeds up when you spray at a specific point you're making the intake mix richer and allowing the engine to run better. seals around the throttle shafts can also be a problem.
never hurts to have a fire extinguisher handy if you're spraying starter fluid around the engine compartment or dumping gasoline into the carb, etc.
The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
Government schooling is about "the perfect organization of the hive."
H.H. Goddard, Human Efficiency (1920)