Taco Bell isn't putting down the chalupa just yet, but it is embarking on a push to shake its reputation as a purveyor of junk food.  The fast-food chain announced yesterday that it's exploring ways to offer more balanced choices and transparency.  CEO Greg Creed said that could mean new products and reformulations of existing ones.  He said Taco bell is testing a range of products this year, with national launches planned for 2014.  The company's Doritos Locos Tacos have been a hit, helping the chain sales at restaurants grow by 8 percent last year.  Taco Bell has about 6,000 locations here in the U.S.