THE MOTORCYCLE DIARIES: A Journey Around South America by Ernesto Che Guevara, translated from the Spanish by Ann Wright (Verso: 155 pp., $11, paperback original). In 1951-52, Che Guevara left his medical studies to bum around South America with a friend. The pair walked, rode a motorcycle and hitched rides through Argentina, Chile, Peru, Colombia and Venezuela. The poverty Guevara witnessed raised his social consciousness, but at 23, he was also a rowdy student who enjoyed drinking, pulling pranks and playing tourist. The good-humored young man who emerges from these pages is strikingly unlike the stern revolutionary icon on the popular poster.