I won't call BS, because a number of factors could have been involved. Did you make any adjustments to the engine? Especially ignition timing? Maybe it quit running on gasoline because it was flooding? Did it use up the hobby fuel faster than gasoline.
Do remember exactly what fuel you used? Brand and Nitro %.
I may be wrong about this...Now you're making me want to try it.
I've got a lot of engines here, and would try it just for grins.
From my own experience...any chance of making it work, would require exactly what Joe said because the air/fuel ratio requirement between the two fuels is completely different.
Fuel Comparison, Gasoline, Methanol, Nitromethane - SMOKEmUP.com
I'm fairly certain that even if you did modify the carbuerator and compression ratio to run nitro, this engine wouldn't last 100 yards.
Hobby fuel is entirely different than what we mix for the race car. Hobby fuel is intended to be used in a high compression 2-cycle diesel.
The fact that yours made enough power to mow the grass is amazing!