Is the world ready for a flaming Nicolas Cage? After a long string of financial flops, this idiosyncratic actor is placing his faith in a comic-book character with a combustible body and an addiction to jelly beans. In ‘‘‘‘Ghost Rider‘‘‘‘ Mr. Cage is Johnny Blaze, a daredevil biker who once made a deal with Mephistopheles (an orange-eyed Peter Fonda) and is now required to hunt down wayward demons while shooting flames from every pore. No wonder he listens to the Carpenters. 　　 But Johnny‘‘s emasculating musical tastes are not the only problem with ‘‘‘‘Ghost Rider,‘‘‘‘ a movie that betrays the promise of its first 30 minutes -- when Johnny is played by the charming young actor Matt Long -- with an increasingly witless script and a star who simply allows the movie to unfold around him. This dissociation leaves the supporting cast to its own devices, with no one suffering more than the appealing Eva Mendes as Johnny‘‘s true love, Roxanne. If Ms. Mendes ever finds a director willing to allow her to perform with her shirts fully buttoned, there will be no stopping her. With its sequel-ready resolution, ‘‘‘‘Ghost Rider‘‘‘‘ embodies franchise hopes that may be dashed by a central character who‘‘s more funny than frightening. As for Mr. Cage, the only thing he should be firing is his manager