Eric B. & Rakim will embark on their first tour in more than 20 years next month. “It’s time to show you,” the duo wrote in a tweet, accompanied by a list of dates beginning April 8 in Boston and running through to a San Francisco on May 3. The tour follows their one-off reunion show last year, which celebrated the 30th anniversary of Paid in Full. Around the time of the reunion, the duo teased that new music was “a definite possibility.”