Thanks for the advice! I'm already very careful with the mixture. Was obvious during first breakin that #1 is the leanest, with the very (very) rich mixture it is the only cilinder that gets luke warm. The others stayed almost completely cold. Now they are almost even.
With my 33cc engine the base setting in the manual is on the rich side. To get all cilinders to fire you have to lean the mixture. This is on the full throttle setting and mid range.
Will maiden this weekend (if all is well). Will try to get some video.