Its from the 1980's era when K.E.Z. owned the "EZ Rider" Orginally ARCO, then Dailex, and through the 1980's K.E.Z. (the giveaway of it bieng that timeframe is is the tab for the numberplate as well as the logo design on the seat. In the catalog I have you could get it with array of engines including briggs, Kawasaki, and Tecumseh ranging from 3 to 5 horsepower.
Markus you must have EVERY ad for every Cool toy I wanted as a kid. I wish this one had the cool paint, but it was long gone before I picked it up for my son in about 1991. I found another newer Tecumseh ohv Enduro 5 horse in the basement. I might go with it or there is the harbor freight 6.5 that is coming out of the Bird mini bike you identified for me. I found a Tecumseh hs50 that will end up in the Bird with a proper belt like the ad you sent me. Thanks again for that!!! Good eye Golden Pinto. No one builds a go kart frame like harbor freight. But with the engine behind the rear wheels it takes 50-70 lbs to keep the front wheels on the ground. Without the weights it is a wheely kart. Lots of fun but doesn't steer worth a darn. This was mach up, ended up hanging the weights off the front end.