Just bought a '68 chevy malibu w/327 ci engine. It has been sitting for quite a while but is in overall good condition. The engine is tough to start and misfires until warm. Then it runs great and starts quickly. If it's just old gas causing the problem, should I have the plugs pulled and cleaned or replaced? Should I do anything with the carburetor? Could it be a more serious problem even if it doesn't misfire when warm? Thanks!