Honda HR214 Vibration

I picked up a Honda HR214 last fall that was in moderate condition. While most of the repairs it needs are straightforward the one thing that worries me is the vibration. When the blade clutch is NOT engaged there is a heavy vibration. When the clutch is engaged and the blades are turning the vibration goes away. My assumption is that the clutch is in need of repair, but before I start in I wanted a second opinion. Is the clutch the likely culprit, or am I wrong? Thanks in advance.