I forget some of the details, but after I bought a Centerforce centrifugal clutch, I started reading forum posts of people having problems with them vibrating. Their centrifugal clutch is a diaphragm type clutch with a ring of weights held in place by a circular wire. The ring of weights results in the centrifugal function and the wire ring is somewhat loose...you can move it about 1/4 of an inch...the geometric center ring can be manually moved +/- 1/4 of an inch relatively to the rotational axis of the input shaft. The idea is that this motion allows the ring to self balance it self. What Centerforce technical support said was that if you have an excessive engine vibration/flywheel imbalance, this vibration will not only prevent the ring from achieving self balance, but the engine vibration will also cause the ring to move in a direction to make the imbalance much worse.
I don't know if the above is applicable to your particular, but it's something everyone should keep in mind I think.