Built around AJS's cross - motocross motorcycle platform, the 1974 AJS Stormer Y4 250 Mk 2 relies on a 247 cc (15.1 cu in) air-cooled single cylinder, two-stroke powerplant. In factory specification, peak output is rated at 25 HP (18.2 kW) at 7,000 rpm, transferring power to the rear wheel through a 4-speed gearbox and chain final drive. With a specific output of 101.2 HP per liter, the engine character is reflecting a performance-oriented street tune that balances strong mid-range pull with an energetic top-end rush.
On the scales, the Stormer Y4 250 Mk 2 measures 104.3 kg (230 lbs) dry, translating to a power-to-weight ratio of 0.24 HP/kg (4.17 kg per horsepower). Rider ergonomics and chassis geometry center around a 762 mm (30 in) seat height — giving shorter riders and urban commuters confident flat-foot reach at traffic stops, combined with a 1,410 mm (55.5 in) wheelbase engineered for quick, flickable steering geometry. The 7.57-liter (2 US gal) fuel tank supports practical everyday commuting and weekend road stints.
Specific Output
101.2 HP/L
Power-to-Weight
0.24 HP/kg (4.17 kg/HP)
Standover Height
762 mm (30 in)
Engine
Displacement247.0 ccm (15.07 cubic inches)
Engine TypeSingle cylinder, two-stroke
Engine DetailsSingle cylinder, two-stroke
Power25.0 HP (18.2 kW)) @ 7000 RPM
Compression11.0:1
Bore x Stroke68.0 x 68.0 mm (2.7 x 2.7 inches)
Fuel SystemCarburettor. AMAL 32mm concentric
Fuel ControlPort control
Ignitionflywheel magneto
LubricationPre-mix. Castrol R at 20:1
CoolingAir
Max RPM8000
Transmission
Gearbox4-speed
Final DriveChain (final drive)
ClutchWet plate Diaphram
Performance
Exhaustloud, expansion chamber
Chassis
Frame TypeDouble downtube, full cradle
Front SuspensionTelescopic forks
Front Travel178 mm (7.0 inches)
Wheelbase1410 mm (55.5 inches)
Ground Clearance254 mm (10.0 inches)
Wheels & Brakes
Front Tyre2.75-21
Rear Tyre4.00-18
Front BrakesExpanding brake (drum brake)
Front Brake Ø127 mm (5.0 inches)
Rear BrakesExpanding brake (drum brake)
Rear Brake Ø127 mm (5.0 inches)
Dimensions & Weight
Dry Weight104.3 kg (230.0 pounds)
Power/Weight0.2396 HP/kg
Seat Height762 mm (30.0 inches) If adjustable, lowest setting.
Fuel Capacity7.57 litres (2.00 US gallons)
Other
StarterKick
Color OptionsOrange tank, grey frame, black side panels
Use this page to compare this motorcycle by its real specifications, not only by model name. Focus on the details that affect fit, comfort, handling, range and ownership.
Power
Compare engine output with similar motorcycles if acceleration, highway use or two-up riding matters.
Seat Height
Check the seat height against your inseam and riding posture before choosing a motorcycle.
Weight
Compare weight carefully because it affects low-speed handling, parking and confidence.
Fuel Capacity
Fuel capacity helps estimate touring range and how often you may need to stop.
Brakes
Brake setup is worth comparing if you ride in traffic, mountains or with a passenger.
Suspension
Suspension details can matter for comfort, road feel and long-distance riding.
Transmission
Transmission and final drive affect maintenance, smoothness and everyday usability.
