Fara
First of all check the spectrum to see if you're getting vibration coming from the prop. Be careful because the prop rpm on the Rotax is very close to the 6th harmonic/multiple of the rotor you may have to reduce engine revs to separate the two.
I often struggle with prop balancing especially with pusher gyros. I recently ended up tying the tail of a gyro down to a block of concrete to stop it from interfering with the balancing.
I also finished by checking the prop balance/vibration in flight which was different to that on the ground.
If you don't have a spinner (prop cone with lots of screws you can use for balancing) you're left with washers on the prop bolts which I really don't like because you're constantly loosening and tightening those bolts. If you have a pre rotator pulley that is hollow on the inside you can stick the lead weights used for balancing car wheels. That's what I do on the ELA.
Make sure you have the latest version of the firmware (.fw) and user interface (UI) from Smart Avionics they added what they call the "spider" for prop balancing which gives you a visual picture of where the "weight sites" are. Chris Buchanan uses the PB4 for props and says it's really helpful, talk to him.
Mike