Main characteristics of the 139QMB engine:

• Engine type: 4-stroke, single-cylinder, forced air cooling.
• Displacement: stock about 49.9 cm³ (registered as a moped on paper), often tuned up to 72–80 cm³.
• Power: about 3.5–5 hp (depending on tuning and displacement).
• Transmission: automatic (belt-driven variator).
• Crankcase oil capacity: about 0.7–0.8 liters needed for a change (10W-40 oil for 4T is recommended).
• Engine life: on average about 20,000 km with timely maintenance.

Features and maintenance:

• Ease of repair: Spare parts (piston kits, belts, variators, carburetors) are widely available and inexpensive.
• Tuning: Replacing the standard piston with a 72 cm³ or 80 cm³ one (piston diameter 47 mm) is popular to improve traction.
• Spare parts: Parts can be found on local marketplaces such as OZON Uzbekistan.
If you have a specific question about this scooter, please clarify:
• What exactly is the fault or problem?
• Are you looking for spare parts or information on repair/tuning?