Hi,
I looked it up this morning.
Energy is very high @~44Mj/Kg ,but requires 14.5Kg Air per Kg Gas for combustion.
So per Kg of Air it gives 44/14.5 = 3Mj energy.
Also v low vaporization temp therefore very hot engine, which in addition causes more expansion of air and gas during intake.
This results in less being burned per stroke = less power.
Remember the '60' 2 strokes ,with long pipe set ups for the vertical pulls, you could hold the cylinder head at full throttle and it stayed cool.
You would not do that with a small gas 2 stroke.

Brian