The later 2 stroke Victa filter housings still have a restrictor in them and work with a Victa 18.
A black spark plug is generally more indicative of a rich fuel mixture or incomplete combustion rather than a weak spark. However, a weak or inconsistent spark can contribute to poor combustion and cause the spark plug to foul more quickly, leading to a black, carbonized appearance.
Some of the tachometers have a spark analyzer that makes it easy to diagnose a faulty coil but cost a little more so it's usually cheaper just to try another coil from a later full crank Victa if you suspect a weak spark after servicing the points and condenser or if you try a module that still looks like a weak spark.
