Of note, this is the "B" model. This is the unit currently in production, and has some improvements over the earlier ones.
The Saito FA-150B is a 4-stroke, glow fuel engine designed for 1/4 scale models. It has the same dimensions and weight as 1.20-size engines, but with 20% more displacement. The FA-150B has the following specifications:
Power: 2.5 horsepower
Displacement: 25cc
Bore: 34mm
Stroke: 27.6mm
Weight: 890g
Recommended prop: 14 x 10 ~ 16 x 8in
Cylinder: AAC
Practical RPM: 2,000 ~ 10,500