the clanking is probably the damper. When the engine runs rough the damper springs start clanking. My dad called me the other day to tell me my boat was making a metal clanking noise at idle in gear. I ordered a new damper. Got out to his place and ran it and found two of the plug wires switched causing a stumble and the damper to talk. switched them back, threw a timing light at it and all is well.