A 150cc scooter will likely top out around 50 to 60 mph, whereas something a lot heavier, such as a 150cc Go Kart will have a much slower top-end speed.
Motor scooters are typically made in three engine sizes, 50, 150 and 250 cubic centimeters. The larger the engine size, the faster it can travel, in most scenarios. A heavier scooter, or a heavier driver, will be a slower scooter. Although bicycles with engines were being built since the end of WWI, it was not until 1952 when a master bicycle maker, Johann Puch, developed what would become the precursor to today's Mopeds, motor scooters and motor cycles.