you have to check the compressor and turbine wheel.
if there is a to easy slight fitt , then thats you problem.
its very simple ,if the turbine engine runs at low rpm , everything is alright but at higher revs ,the compressor go's out of the center ,because of the loose fitt.
i dont know if you have this , but i just give you a idea of what can be wrong.
balancing is very simple.
take a roll of tape ,and thats your balancing wheight.
take the engine apart ,and then you only must put the shaft, turbine wheel and spacer, compressor ,and compressor nut in de shaft tunnel, with the bearings offcourse.

then hold the tunnel near the turbine wheel with two fingers ,and spin the wheel with pressed air.
you will feel vibration.
no worries, put a piece of duc tape some where on the wheel ,not the blades.
devide the turbine wheel in 6 marks, mark them with a pen , or what ever , if there are marks ,its oke.
then put the tape each time on another mark ,and you will see ,the vibration will be less .
you have to practice a little ,but its realy good balancing.
if you have found the places of vibration , then slightly grind the spot at the opposite site away on the ring of the wheel.

I use the spinner nut for balancing the compressor.

I you have problems ,just ask me.

good luck.

Martin.