Having looked closely at picture, rear brake right-hand side flat tank, engine I'm fairly certain is a Swiss MAG motor. This was a proprietary brand (similar to Blackburn, JAP, Villiers, etc.). One just had to make a frame and then stick your name on the petrol tank. I'll take a guess that it's a late '20s, possibly German (Condor or Standard) but these were used by Belgian and I think French manufacturers.
Regards, Geoff