Weird Science - Season 4 Episode 11 By the Time We Got to Woodstock

After Gary and Wyatt wish that they could time travel, the wish goes bad and they end up stuck in 1969 along with Lisa. After six months of being in the past, they realize that Lisa can't remember anything. She thinks that she's a hippie on her way to Woodstock. Wyatt and Gary need to get across the country and fix Lisa's memory or be stuck in the hippie age. Wyatt, Gary, and Chett all go on a road trip across the country, even meeting the future president.