wobble when flying cb100 with scale hughes fuse

[Cthulu]

hi folks. I finally got round to finishing a hughes 500 build on my walkera cb100. I took it into a hover for the first time and noticed there is quite a serious wobble when any movements are made. Its a fairly new CB100 so it shouldn't be the main gear. I had to make some adjustments to the fuselage to get the heli to correctly fit inside, and as such, Ive noticed that if the main blades and rotor hub are lined up parallel over the tail boom there is a slight overlap (3mm or so) where the main blades rotor disc will overlap the tail rotor disk when in flight ( they wont connect, the main blades sit a cm or 2 above the max height of the tail rotor). Can any of you folks tell me if it could be the downwash from the main blades affecting the tail rotor, causing a wobble? This is what i thought it could be. Or any other suggestions? Any help greatly appreciated.
cheers,
Liam

[acwman]

could it be that your head speed is too low..? try increasing the headspeed and see if it goes.

[Cthulu]

not the headspeed

tried increasing the headspeed and it damped it down a bit but it is still way too prominent to be fixed by just that. Does anyone know if what i mentioned previously could affect it? If the main rotor disk overlaps the tail rotor disk, could that not be applying downward force on the edge of the tail rotor disk, causing the wobble?