Hi there,
Have you checked for condensation in the distributor cap? It could be a definite possibility condsidering your symptoms. Another thing I would check is the resistance of the spark plug and distributor - coil wires. You should measure from about 9,000 ohms to no more than 20,000 ohms through each wire. If any of them measures infinite, or open, you have found a problem! Many new wires will fail soon due to the poor ends they install these days on aftermarket wiring kits. Another thing to check for is any signs of carbon traces around the high tension socket on the coil. Try replacing the condensor, they are cheap. A last thing to check is the point gap, if it has points. The gap should be such that the pattern the wiper arm makes on the points cam is about evenly divided between make and break. The car will always run smoothly if the pattern is in that area. If the distributor shaft bushings are worn badly it is sometimes difficult or impossible to make an engine run well.
Richard Wooldridge