Wall St set to open flat as Yellen's speech awaited

Wall Street was set to open little changed on Friday as cautious investors braced for a speech by Federal Reserve Chair Janet Yellen for further clues on the timing of interest rate hikes. Yellen is due to speak at an event hosted by Harvard University at 1:15 p.m. ET (1715 GMT). A rate hike in June was seen as highly unlikely until recently.