Microlighters

We are busy experimenting wit a warp drive on our Bush Baby. At the moment we are using an over pitched wooden prop. The warp drive is performing well, but on declerating, The is quit a bad vibration. Can anyone tell me what might be the cause?
Thanks.

Does it happen at certain revs?

What engine you have?

Are all the blades pitched exactly the same?

Yes critical that all the blades are exactly the same pitch.

Also check the balance of the blade.

Check balance:

Tie rope to middle of a pen or stick, tie other end of rope to a branch, push the pen thru the middle of prop and let it hang. If balanced prop should be level

Thanks all.
The motor is 912 Extra.
Vibration is at any rpm when throttling back.
The problem is being sorted out. Buying a new De Necker prop.