The team also won the Uhrencup that year and Muhmenthaler scored the first goal in the final, as they beat FC Basel 3–1.
[2] In the summer of 1972, Muhmenthaler transferred to BSC Young Boys and he played there as forward for three years.
With the Young Boys, Muhmenthaler won the Uhrencup 1973 and he scored a goal in the semifinal against his previous club Grenchen.
He made his team debut in the 5–1 home win against Grasshopper Club Zürich and Muhmenthaler scored three of the goals.
Amongst these he describes as one of his personal highlights the 1998 FIFA World Cup qualification match on 11 November 1997 between Italy and Russia (1–0) in front of 80 000 spectators at the Stadio San Paolo, Naples.