go back on vs go west

go back on

verb
  • Used other than figuratively or idiomatically: see go, back, go back, on. 

  • to fail to keep; to renege on. 

  • to be treacherous or faithless to; betray. 

go west

verb
  • Used other than figuratively or idiomatically: see go, west. 

  • Synonym of set: to move toward the western horizon, to go down. 

  • To move to the American West, particularly (historical) during the 19th century era. 

How often have the words go back on and go west occurred in a corpus of books? (source: Google Ngram Viewer )