How Fast Can a 50cc Scooter or Moped Go?

Chinese scooters that feature the 139QMB 50cc Honda-clone engine have a limited stock speed of around 30-35 miles per hour. The 2-stroke 1E40QMB 50cc engine can propel a small-frame scooter up to 45 miles per hour, as well.

Restrictions in the scooter's exhaust, CVT transmission and ignition box (also referred to as a CDI box) can inhibit speed and engine power. Implementation of one or many of these restrictions can vary from manufacturer to manufacturer.

Many scooter enthusiasts who wish to squeeze more power out of their 50cc will first check the CVT for a restriction ring that limits the variator plate travel. Removing the variator restrictor ring requires removal of the CVT case cover, kick start lever and variator plate. This modification can usually yield a few miles an hour top speed.

Another restriction ring may be present between the exhaust pipe flange and the cylinder head exhaust port. The removal process for the exhaust restriction on a 50cc scooter is fairly straightforward and only requires metric socket set to complete. Having a less restrictive exhaust will boost the scooters power, responsiveness and acceleration capability.

For certain 50cc 139QMB scooters, disconnecting a pink-colored wire connected to the CDI box will disable the engine's RPM limiter. The CDI can be found near the battery, or mounted on the frame. Depending upon the weight of the rider, road conditions and CVT tuning- scooters with a derestricted CDI can possibly reach speeds of over 50 miles per hour.

Combine the derestriction methods listed above, with a free-flow aftermarket air filter, upgraded carburetor main jet and a big bore kit, a 139qmb 4-stroke (For example) can reach speeds of over 55-miles per hour on a flat surface.

Big bore kits for a 50cc 139QMB or 2-stroke 1E40QMB 50cc can increase the displacement of these engines dramatically. The increased displacement from a scooter big bore kit will produce an extraordinary amount of power, but requires a fair amount of mechanical ability to install.

Upgrades to a scooter's CVT roller weights and the clutch contra spring will also improve drivability, acceleration and top speed.

Learn more about performance parts for Chinese made scooters here.