Harley-Davidson Topper

The Topper had a 165 cc (10.1 cu in) single-cylinder two-stroke engine mounted horizontally between the floorboards.^[1] The engine required a premixed gasoline/oil mixture. The starter was of the rope-recoil type similar to lawnmowers^[1][7] or the Lambretta E model.^[8] Unlike most scooters with enclosed engines, the Topper's engine did not have a cooling fan.^[1][4][5] It was expected that the low, horizontally-mounted engine would be cooled by air passing under the scooter,^[1] but some Toppers developed overheating problems.^[4] The engine used a reed valve in its induction system.^[2]