Yesterday, I got the Fuji 099S-II baffle piston ABC engine with low 5.5:1 compression to run through a whole tank of fuel yesterday. This was with the synthetic oil based O'Donnell 30% Nitro Heli Fuel.
It sat in a drawer for the past two decades, because I could not get it to run reliably. I replaced it with an OS Max 15FPS ("S" = CL version) on a Junior Ringmaster, which would run reliably.
Details of this unique and fairly rare engine are in:
and Message #228,
Looks like the trick to get it running was high nitro fuel and a hot plug.