Yakamochi's strength as a politician is demonstrated by the fact that although he was promoted to Sangi (councilor) in 780, he was expelled from the capital after being suspected of involvement in HIKAMI no Kawatsugu's plot (HIKAMI no Kawatsugu's Rebellion).
宝亀11年（780年）、参議に昇進したものの、氷上川継の謀反事件（氷上川継の乱）に関与を疑われて都を追放されるなど、政治家として骨太な面を見ることができる。