It doesn't take Sherlock Holmes to deduce that Eighteen Weapons of Kung Fu is a martial arts film. Nor does one have to sit through the film's 86 minutes to determine that it's a "Ninja vs. the Bad Guys" affair. This time, the heroes are even better armed than usual. Trouble is, so are their enemies. Enjoyably predictable, Eighteen Weapons of Kung Fu has been made available on video in an unrated version by Best Films & Video Corporation.