These are the known mechanical and performance specifications for your 1987 ATK NX 250.
Basic Specs

Engine
Displacement249.00 ccm (15.19 cubic inches)
Type
DetailsSingle cylinder, four-stroke
Max RPM
Compression
Bore/Stroke
Valves/Cylinder4
FuelingCarburettor. Keihin 24mm
IgnitionCDI
ExhaustSupertrapp
Lubricationwet sump
CoolingLiquid
Fuel Economy & Polution
Fuel Consumption
Fuel Capacity8.70 litres (2.30 gallons)
Emissions
Chassis
Frame Type
Rake
Trail
Front SuspensionWP USD
Front Travel
Rear SuspensionWP Multi Adjuster Shock
Rear Travel
Seat
Seat Height
Alt. Seat Height940 mm (37.0 inches) If adjustable, highest setting.
Total Height
Total Length1,473 mm (58.0 inches)
Total Width820 mm (32.3 inches)
Ground Clearance323 mm (12.7 inches)
Wheelbase1,473 mm (58.0 inches)
Dry Weight128.0 kg (282.2 pounds)
Wet Weight
Wheels & Brakes
Front Tire/Tyre80/100-21
Rear Tire/Tyre100/100-18
Front BrakesSingle disc. 2-piston calipers
Front Brake Diameter24 mm (0.9 inches)
Rear BrakesExpanding brake (drum brake)
Rear Brake Diameter
Wheels
Comments
Uses a Honda 4-stroke engine.