RE: 2 stroke vs 4 stroke
I think OS is changing things up a little with their new AX series, they seem to be designed more for low end torque. Compare specs on the same displacement and I think the 2 stroke has a definite edge.
OS 120AX
Displacement: 1.218 cu in (19.96cc)
Bore: 1.197" (30.4mm)
Stroke: 1.083" (27.5mm)
Crankshaft thread size: 5/16-24
Practical RPM: 1,800 - 9,500 RPM
Power Output: 3.1ps/9000 RPM
Weight: 22.82oz (647g)
7.074oz (219.2g) with 90° adapter installed
7.907oz (245g) with extension installed
Propeller: 15x10-12 or 16x8-10
OS FS-120 III Surpass
Bore: 30.4mm (1.20")
Stroke: 27.5mm (1.08")
Power Output: 2.1 BHP at 12,000 RPM
Practical RPM Range: 2,000 - 12,000 RPM
Weight-Without Muffler: 32.5oz (921g)
Weight-With Muffler: 35.3oz (1000g)
Crankshaft Thread Size: 5/16-24
Valve Clearance: Between .04mm and .1mm (or between .0015" and .004",
measured between the valve tip and rocker arm)
Length: 102mm (4.09") from backplate to the front of the drive washer
Width: 47mm (1.85") width of engine neglecting the mounting flanges
58mm (2.28") distance between the mounting hole centers
Height: 139.5mm (5.49")
Suggested Prop(s): 14x9, 14x10, 14x11, 15x8, 15x9, 15x10, 16x6,
Construction: Aluminum and Aluminum alloys
In this case the 2 stroke is lighter, spins the same prop sizes, and has a lower practical RPM range. As far as burning fuel more efficiently however a 4 stroke will always be top dog, so buy the 4stroke and save money later or buy the 2 stroke a save money now.