Measured the compression rate.
It turnout to be nice and tight, perhaps not a real race specification but 9,5cc headvolume with a 0,8mm squish is good enough to get some decent power.
Angular the bike so the engine is as level as it can be
Set the piston at his top position
Measured the volume
Measured 11,8cc till top plug hole.
11,8cc -2,3cc (plug hole it self)= 9.5cc volume
That is a compression rate close to 7,4 : 1