Looks like a BSA Winged Wheel, about 70cc if I remember correctly and I note the bike folded up for transport in a car or similar.
I had. Minimotor add on, which was a 50cc 2-stroke engine, with it's drive pulley, pressing on the rear tyre.
I remember making various pulleys with different type of knurled finishes, to improve the friction properties between the pulley and the tyre, guaranteed to rip the tyre to shreds in no time!!!