Turns out it was a simple fix. The needle valve was just set way to rich. Once it was adjusted down one whole turn the engine was producing around 8800 rpm no problem at all. (Thanks Jeff for your experience and help).
Managed to get the tail wheel re-soldered to. Looks like it will be a much stronger connection. Next step, final balancing (again) and its ready for the maiden!
Looks like I am going to need a bigger car. Thanks Sandy for the minivan!