High HC readings are the result of un-burnt fuel, usually from ignition system problems. First when a engine has high mileage have the compression tested to make sure that engine is in good working order. If that checks out O.K. then consentrate on the ignition system, any slight misfire wil cause the high H.C. readings that the car has.
If the engine is burning oil this will raise the HC reading also. Sometimes changing the oil will help(fuel in the oil).