Congratulations to fallingdown4u, who was the first to correctly identify this as a 1926 Harlette-Geco – specifically the 175cc Super Sport!
This is one of a few bikes being auctioned off next week at the Bonhams Bonmont Sale in Cheserex, Switzerland (short preview coming later today). Bonhams estimates a value of $3,700-$4,000 but it will be offered with no reserve.
Per the Bonhams description, the Harlette brand was created by the southern French importer of Harley-Davidsons. They didn’t just borrow the name, they also borrowed the green color that was closely associated with H-Ds at the time. The bikes were built by J & H Gerkinet & Co, hence the “Geco” part of the name. Production started in 1924 with a 125cc two-stroke from Gillet-Herstal, and two years later the model got a 175cc Zurcher four-stroke.