Below are the specs given by Novarossi on the 528XSP:
Displacement: 4.66 cm^3
Maximum power: 2.80
RPM: 32.000
Bore x Stroke: 18.35 mm x 17.60 mm
Ports: 3
Piston: CNC machined
Crankshaft: Ø 14 mm
Crank Type: SG Pull-starter
Glow Plug Type: Standard
Exhaust Type: Rear
Carburetor: Ø 8 mm (interchargeable insert)
Carb Type: Slide
Carb Material: Nylon