This is some of the info I received from a member on TheCabe.com, Triped777,
this is a Cyclemotor engine with incorrect exhaust pipe and gas tank from a German motorbike whose name I cannot recall. The tank decal is not correct for the tank. Cyclemotor Company evolved into Evans.
And then later, this:
Not sure of year of bike. Motor probably between 1916 and 1918. If the motor has a single row chain on the flywheel/magneto its the earlier; if it has a double row chain its more toward 1918. This bike is however, a beautiful piece. the exhaust pipe was never secured well from the factory, so its plausible that an original owner may have replaced it with something similar. Likeswise, the bike probably fell over frequently and perhaps the tank had been damaged in the early years and needed replacement. Who knows?? This is still a beautiful re-creation of what once was. The earliest Evans (1918) shared the double row chain motor with the Cyclemotor kit which sold separately. Then Evans upgraded the motor and chasis for the Evans Power Cycle. The later Evans had a different carburetor, decompressor moved from top to the side of the cylinder, different magneto, different flywheel, etc. If you google 1918 Evans, you will see all over the internet, a Cyclemotor kit on an early Davis type bicycle. They put the picture of this "Evans" on coffee mugs to sell. Smiths Autocycle in England ended up with this bike advertised as an Evans, and apparently it is presently in a museum in Germany displayed as "Evans." It is NOT an Evans. It was MY bike that I assembled from pieces, with a beautiful original paint Evans tank, Whizzer sheave, unknown make brass throttle, motor mounts that are clamps from hardware store made for electrical conduit, etc. It's all still on there! Laugh every time I see it. Your bike is a beauty; enjoy it. I sure do!