Hi!
I have flown my GP GEE BEE R-2 (powered by a MVVS 15cc engine with 14x6 APC prop) and it flyes really good. weight is 5kg (11lbs)
It is very important that the CG is right. The instructions say 70mm from the leading edge and this is the what it should be.
Firts I flew the plane with the CG at 85mm ...and it was slightly tailheavy and rather hard to land , moved it to 75mm and it was better..... moved it still furter forward to 70mm and landing was much easier pretty much like any other low winged airplane.
This is a ship that requiers to be balanced like the instruction says....and dont forget to balance it in axial level as well! And do keep it light!
I have Dremeled away all unnecessary glassfibre surfaces and taken up holes in the rear part of the fuselage where the siderudder is and moved every thing as far forward as possible...no lead used.

Regards!
Jan K
Sweden