Motor 1FZ problem with cylinders 3 and 4

[Victor John]

I have a 1993 6 cylinder carbureted cruiser. For several weeks I have been trying to diagnose a problem with the sparkplugs in cylinders 3 and 4 becoming black and the motor misses when trying to accelerate.
I have had a mechanic clean the carburetor and have changed the plugs. How could I know of the problem is with the cables or the distributor or the carburetor? I don't have enough money to start changing parts.