The white color of the spark plugs suggests that you probably have a vacuum leak somewhere. Air is getting into the engine without going through the carburetor, which is making the fuel to air mixture too lean. One possibility would be the carburetor being loose on the intake manifold. Another might be looseness between the intake manifold and the cylinder head, or a large vacuum line being disconnected. Try using a gas source such as a Propane or acetyline torch with the fuel gas flowing without being lit, and pass it around all the gasket surfaces, looking for a place where the engine speed increases or the engine begins to run smoother as the gas is drawn into the vacuum leak. Other possibilities might be very late ignition timing due to a the distributor adjustment getting loose, but that would not account for the condition of the spark plugs.
Jerry
