These are the known mechanical and performance specifications for your 1998 Yamaha ST 125.
Basic Specs

Engine
Displacement125.00 ccm (7.63 cubic inches)
Type
DetailsSingle cylinder, two-stroke
Max RPM11000
Compression
Bore/Stroke
Valves/Cylinder
FuelingCarburettor. mikuni
Ignitionelectronic
Exhaustsingle expansion chamber and muffler
Lubricationoil injection
CoolingLiquid
Performance
Horespower36.00 HP (26.3 kW)
Torque
Top Speed160.0 km/h (99.4 mph)
Fuel Economy & Polution
Fuel Consumption8.00 litres/100 km (12.5 km/l or 29.40 mpg)
Fuel Capacity10.00 litres (2.64 gallons)
Emissions185.6 CO2 g/km. (CO2 - Carbon dioxide emission)
Chassis
Frame Typesteel deltabox
Rake
Trail
Front Suspensionrwu forks
Front Travel
Rear Suspensionmonoshock
Rear Travel
Seat
Seat Height
Alt. Seat Height
Total Height
Total Length
Total Width
Ground Clearance
Wheelbase
Dry Weight110.0 kg (242.5 pounds)
Wet Weight
Wheels & Brakes
Front Tire/Tyre
Rear Tire/Tyre
Front BrakesSingle disc. twin piston caliper
Front Brake Diameter
Rear BrakesSingle disc. twin piston caliper
Rear Brake Diameter
Wheels
Comments
made by Yamaha Thailand model code 4XC