These are the known mechanical and performance specifications for your 1981 Yamaha XJ 400 Seca.
Basic Specs

Engine
Displacement398.00 ccm (24.29 cubic inches)
Type
DetailsFour cylinder boxer, four-stroke
Max RPM
Compression9.7:1
Bore/Stroke51.0 x 48.8 mm (2.0 x 1.9 inches)
Valves/Cylinder
FuelingCarburettor. 2x34 Mikuni
IgnitionBattery Powered Inductive
Exhaust
Lubrication
CoolingAir
Performance
Horespower45.00 HP (32.8 kW)
Torque33.90 Nm (3.5 kgf-m or 25.0 ft.lbs)
Top Speed162.5 km/h (101.0 mph)
Chassis
Frame Type
Rake
Trail
Front Suspension35mm Telescopic Forks
Front Travel142 mm (5.6 inches)
Rear Suspension Single Adjustable Spring Preload
Rear Travel96 mm (3.8 inches)
Seat
Seat Height
Alt. Seat Height
Total Height
Total Length
Total Width
Ground Clearance
Wheelbase
Dry Weight176.0 kg (388.0 pounds)
Wet Weight
Wheels & Brakes
Front Tire/Tyre-19
Rear Tire/Tyre110/90-18
Front BrakesSingle disc. 1 Piston Caliper
Front Brake Diameter
Rear BrakesExpanding brake (drum brake)
Rear Brake Diameter
Wheels
Comments