At the Value Investing Congress in New York, hedge-fund manager David Einhorn, who helps oversee $7.7 billion as president of Greenlight Capital, said Chipotle Mexican Grill’s valuation is too high and he expects it will face challenges from Yum Brands’ Taco Bell chain. Chipotle trades for about 36 times earnings, compared with a multiple of 14.7 for the S&P 500. It posts earnings Oct. 18.